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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                             -----------------------

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934

                                (Amendment No.1)*

                             -----------------------

                            Monaco Coach Corporation
                            ------------------------
                                (Name of Issuer)

                                  Common Stock
                                  ------------
                         (Title of Class of Securities)

                                    60886R103
                                    ---------
                                 (CUSIP Number)

                                December 31, 2003
                                -----------------
             (Date of Event Which Requires Filing of this Statement)

            Check the appropriate box to designate the rule pursuant
                        to which this Schedule is filed:

                                [X] Rule 13d-1(b)

                                [ ] Rule 13d-1(c)

                                [ ] Rule 13d-1(d)

                             -----------------------

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).

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                               Page 1 of 10 pages

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--------------------------                           ---------------------------
CUSIP No. 60886R103                    13G                    Page 2 of 10 Pages
--------------------------                           ---------------------------

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1    NAME OF REPORTING PERSON S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

     Columbia Wanger Asset Management, L.P. 36-3820584

--------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                         (a) [ ]
     Not  Applicable
                                                                         (b) [ ]
--------------------------------------------------------------------------------
3    SEC USE ONLY

--------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware

--------------------------------------------------------------------------------
      NUMBER OF     5    SOLE VOTING POWER
                                           None
       SHARES
                    ------------------------------------------------------------
    BENEFICIALLY    6    SHARED VOTING POWER
                                      1,495,000
      OWNED BY
                    ------------------------------------------------------------
        EACH        7    SOLE DISPOSITIVE POWER
                                           None
      REPORTING
                    ------------------------------------------------------------
     PERSON WITH    8    SHARED DISPOSITIVE POWER
                                      1,495,000
--------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

          1,495,000
--------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

          Not Applicable                                                     [ ]
--------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

          5.1%
--------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON

          IA
--------------------------------------------------------------------------------

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--------------------------                           ---------------------------
CUSIP No. 60886R103                    13G                    Page 3 of 10 Pages
--------------------------                           ---------------------------

================================================================================
1    NAME OF REPORTING PERSON
     S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

     WAM Acquisition GP, Inc.
--------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                         (a) [ ]
     Not Applicable
                                                                         (b) [ ]
--------------------------------------------------------------------------------
3    SEC USE ONLY

--------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware

--------------------------------------------------------------------------------
      NUMBER OF     5    SOLE VOTING POWER
                                           None
       SHARES
                    ------------------------------------------------------------
    BENEFICIALLY    6    SHARED VOTING POWER
                                      1,495,000
      OWNED BY
                    ------------------------------------------------------------
        EACH        7    SOLE DISPOSITIVE POWER
                                           None
      REPORTING
                    ------------------------------------------------------------
     PERSON WITH    8    SHARED DISPOSITIVE POWER
                                      1,495,000
--------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

          1,495,000
--------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

          Not Applicable                                                     [ ]
--------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

          5.1%
--------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON

          CO
--------------------------------------------------------------------------------

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--------------------------                           ---------------------------
CUSIP No. 60886R103                    13G                    Page 4 of 10 Pages
--------------------------                           ---------------------------

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1    NAME OF REPORTING PERSON
     S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

     Columbia Acorn Trust
--------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                         (a) [ ]
     Not  Applicable
                                                                         (b) [ ]
--------------------------------------------------------------------------------
3    SEC USE ONLY
--------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     Massachusetts
--------------------------------------------------------------------------------
      NUMBER OF     5    SOLE VOTING POWER
                                           None
       SHARES
                    ------------------------------------------------------------
    BENEFICIALLY    6    SHARED VOTING POWER
                                      1,495,000
      OWNED BY
                    ------------------------------------------------------------
        EACH        7    SOLE DISPOSITIVE POWER
                                           None
      REPORTING
                    ------------------------------------------------------------
     PERSON WITH    8    SHARED DISPOSITIVE POWER
                                      1,495,000
--------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     1,495,000
--------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

     Not Applicable                                                          [ ]
--------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

     5.1%
--------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON

     IV
--------------------------------------------------------------------------------

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Item 1(a) Name of Issuer:
          Monaco Coach Corporation

Item 1(b) Address of Issuer's Principal Executive Offices:

          91320 Industrial Way
          Coburg, Oregon  97408

Item 2(a) Name of Person Filing:

          Columbia Wanger Asset Management, L.P. ("WAM")
          WAM Acquisition GP, Inc., the general partner of WAM
          ("WAM GP")
          Columbia Acorn Trust ("Acorn")

Item 2(b) Address of Principal Business Office:

          WAM, WAM GP and Acorn are all located at:

          227 West Monroe Street, Suite 3000
          Chicago, Illinois  60606

Item 2(c) Citizenship:

          WAM is a Delaware limited partnership; WAM GP is a Delaware
          corporation; and Acorn is a Massachusetts business trust.

Item 2(d) Title of Class of Securities:

          Common Stock

Item 2(e) CUSIP Number:

          60886R103

Item 3    Type of Person:

          (d)  Acorn is an Investment Company under section 8 of the Investment
               Company Act.

          (e)  WAM is an Investment Adviser registered under section 203 of the
               Investment Advisers Act of 1940; WAM GP is the General Partner of
               the Investment Adviser.

                               Page 5 of 10 pages

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Item 4    Ownership (at December 31, 2003):

          (a) Amount owned "beneficially" within the meaning of rule 13d-3:

              1,495,000

          (b) Percent of class:

              5.1% (based on 29,093,637 shares outstanding as of September 27,
              2003).

          (c) Number of shares as to which such person has:

              (i)  sole power to vote or to direct the vote: none
              (ii) shared power to vote or to direct the vote: 1,495,000
              (iii) sole power to dispose or to direct the disposition of: none
              (iv) shared power to dispose or to direct disposition of:
                   1,495,000

Item 5    Ownership of Five Percent or Less of a Class:

          Not Applicable

Item 6    Ownership of More than Five Percent on Behalf of Another Person:

          The shares reported herein have been acquired on behalf of
          discretionary clients of WAM, including Acorn. Persons other than WAM
          and WAM GP are entitled to receive all dividends from, and proceeds
          from the sale of, those shares. Acorn is the only such person known to
          be entitled to all dividends from, and all proceeds from the sale of,
          shares reported herein to the extent of more than 5% of the class.

Item 7    Identification and Classification of the Subsidiary Which Acquired the
          Security Being Reported on by the Parent Holding Company:

          Not Applicable

Item 8    Identification and Classification of Members of the Group:

          Not Applicable

Item 9    Notice of Dissolution of Group:

          Not Applicable

                               Page 6 of 10 pages

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Item 10 Certification:

     By signing below I certify that, to the best of my knowledge and belief,
the securities referred to above were acquired and are held in the ordinary
course of business and were not acquired and are not held for the purpose of or
with the effect of changing or influencing the control of the issuer of the
securities and were not acquired and are not held in connection with or as a
participant in any transaction having that purpose or effect.

                               Page 7 of 10 pages

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                                    Signature
                                    ---------

     After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

Date:  February 10, 2004

          The undersigned corporation, on the date above written, agrees and
          consents to the joint filing on its behalf of this Schedule 13G in
          connection with its beneficial ownership of the security reported
          herein.

                                        WAM Acquisition GP, Inc.
                                           for itself and as general partner of
                                           COLUMBIA WANGER ASSET
                                           MANAGEMENT, L.P.


                                        By: /s/ Bruce H. Lauer
                                            ------------------------------------
                                            Bruce H. Lauer
                                            Senior Vice President and Secretary

          The undersigned trust, on the date above written, agrees and consents
          to the joint filing on its behalf of this Schedule 13G in connection
          with its beneficial ownership of the security reported herein.

                                        COLUMBIA ACORN TRUST


                                        By: /s/ Bruce H. Lauer
                                            ------------------------------------
                                            Bruce H. Lauer
                                            Vice President, Treasurer and
                                            Secretary

                               Page 8 of 10 pages

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                                  Exhibit Index

Exhibit 1 Joint Filing Agreement dated as of February 10, 2004 by and among
          Columbia Wanger Asset Management, L.P., WAM Acquisition GP, Inc. and
          Columbia Acorn Trust.

                               Page 9 of 10 pages

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                                                                       EXHIBIT 1

                             JOINT FILING AGREEMENT

     The undersigned hereby agree to the joint filing of the Schedule 13G to
which this Agreement is attached.

          Dated:  February 10, 2004

                                        WAM Acquisition GP, Inc.
                                           for itself and as general partner of
                                           COLUMBIA WANGER ASSET
                                           MANAGEMENT, L.P.


                                        By: /s/ Bruce H. Lauer
                                            ------------------------------------
                                            Bruce H. Lauer
                                            Senior Vice President and Secretary


                                        COLUMBIA ACORN TRUST


                                        By: /s/ Bruce H. Lauer
                                            ------------------------------------
                                            Bruce H. Lauer
                                            Vice President, Treasurer and
                                            Secretary

                               Page 10 of 10 pages


