Exhibit 10.21(o)

NOTE: PORTIONS OF THIS EXHIBIT INDICATED BY “[****]” ARE SUBJECT TO A CONFIDENTIAL TREATMENT REQUEST, AND HAVE BEEN OMITTED FROM THIS EXHIBIT. COMPLETE, UNREDACTED COPIES OF THIS EXHIBIT HAVE BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION AS PART OF THIS COMPANY’S CONFIDENTIAL TREATMENT REQUEST.

FOURTH AMENDMENT TO AMENDED AND RESTATED

INVENTORY FINANCING AGREEMENT

THIS FOURTH AMENDMENT (the “Amendment”) dated this 29^th day of August, 2014, is to that certain Amended and Restated Inventory Financing Agreement entered into by and among GE Commercial Distribution Finance Corporation (“CDF”) and the undersigned Dealers (each, individually, a “Dealer” and, collectively, “Dealers”) dated June 28, 2013 (as amended, supplemented or otherwise modified form time to time, the “Financing Agreement”).

WHEREAS, the parties hereto desire to amend the Financing Agreement in certain respects;

NOW THEREFORE, in consideration of the premises and of other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged by the parties, the parties hereby agree as follows:

1. Exhibit A of the Financing Agreement is hereby amended and restated in its entirety in form and substance as set forth in Exhibit A hereto.

2. Section 1(b) of the Financing Agreement is hereby amended to replace “two hundred five million dollars ($205,000,000.00)” with “two hundred thirty-five million dollars ($235,000,000.00),” as the “Maximum Credit Amount” defined therein.

3. Section 1(c) of the Financing Agreement is hereby deleted in its entirety and replaced with the following:

Pre-Owned Inventory Advances and Sublimits. Subject to the overall Maximum Credit Amount set forth above and the terms and conditions of this Agreement, on and after the date hereof (the “Closing Date”), CDF agrees to make cash advances to Dealers with respect to pre-owned units of inventory; provided that such cash advances shall not exceed the Pre-Owned Inventory Sublimit and must comply with the pre-owned inventory advance terms set forth herein. Regardless of the amount of credit available to Dealers under the Maximum Credit Amount hereunder, CDF shall not provide extensions of credit to Dealers in excess of forty-five million dollars ($45,000,000.00) with respect to used or pre-owned inventory (the “Pre-Owned Inventory Sublimit”). Within such Pre-Owned Inventory Sublimit, (A) any advances with respect to units with applicable valuations of five hundred thousand dollars ($500,000.00) or more shall require unit specific documentation (including an advance request form), (B) CDF will not advance Dealers more than thirty-five million dollars ($35,000,000.00) of such Pre-Owned Inventory Sublimit for used or pre-owned inventory with applicable valuations of less than five hundred thousand dollars ($500,000.00) (the “Other Pre-Owned Sublimit”), and (C) CDF will not advance Dealers more than twenty million dollars ($20,000,000.00) of such Pre-Owned

KCP-4504921-5

NOTE: PORTIONS OF THIS EXHIBIT INDICATED BY “[****]” ARE SUBJECT TO A CONFIDENTIAL TREATMENT REQUEST, AND HAVE BEEN OMITTED FROM THIS EXHIBIT. COMPLETE, UNREDACTED COPIES OF THIS EXHIBIT HAVE BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION AS PART OF THIS COMPANY’S CONFIDENTIAL TREATMENT REQUEST.

Inventory Sublimit for used or pre-owned inventory with applicable valuations of five hundred thousand dollars ($500,000.00) or more (the “Specific Pre-Owned Sublimit”).

4. Section 5(b)(viii) of the Financing Agreement is hereby amended to replace “eight million dollars ($8,000,000.00)” with “nine million dollars ($9,000,000.00),” as used therein.

5. Section 17 of the Financing Agreement is hereby amended to replace “June 28, 2016” with “August 29, 2017,” as used therein.

6. Each reference in the Financing Agreement, [****], the Program Terms Letter, and any other document, instrument or agreement related thereto or executed in connection therewith (collectively, the “Documents”) to the Financing Agreement shall be deemed to refer to the Financing Agreement as amended by this Amendment. Capitalized terms used but not otherwise defined herein shall have the meanings assigned to them in the Financing Agreement.

7. Each Dealer hereby ratifies and confirms the Financing Agreement, as amended hereby, and each other Document executed by such Dealer in all respects.

8. This Amendment shall be binding upon, inure to the benefit of and be enforceable by the parties hereto and their participants, successors and assigns.

9. This Amendment may be executed in any number of counterparts, each of which counterparts, once they are executed and delivered, shall be deemed to be an original and all of which counterparts, taken together, shall constitute but one and the same agreement. This Amendment may be executed by any party to this Amendment by original signature, facsimile and/or electronic signature.

KCP-4504921-5

NOTE: PORTIONS OF THIS EXHIBIT INDICATED BY “[****]” ARE SUBJECT TO A CONFIDENTIAL TREATMENT REQUEST, AND HAVE BEEN OMITTED FROM THIS EXHIBIT. COMPLETE, UNREDACTED COPIES OF THIS EXHIBIT HAVE BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION AS PART OF THIS COMPANY’S CONFIDENTIAL TREATMENT REQUEST.

IN WITNESS WHEREOF, the parties hereto have duly executed this Amendment as of the date first above written.

MARINEMAX, INC.

By: MARINEMAX EAST, INC., the sole member of Boating Gear Center, LLC

KCP-4504921-5

NOTE: PORTIONS OF THIS EXHIBIT INDICATED BY “[****]” ARE SUBJECT TO A CONFIDENTIAL TREATMENT REQUEST, AND HAVE BEEN OMITTED FROM THIS EXHIBIT. COMPLETE, UNREDACTED COPIES OF THIS EXHIBIT HAVE BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION AS PART OF THIS COMPANY’S CONFIDENTIAL TREATMENT REQUEST.

By: MARINEMAX, INC., the sole member of My Web Services, LLC

By: MARINEMAX EAST, INC., the sole member of MarineMax Charter Services, LLC

GE COMMERCIAL DISTRIBUTION FINANCE CORPORATION

KCP-4504921-5

NOTE: PORTIONS OF THIS EXHIBIT INDICATED BY “[****]” ARE SUBJECT TO A CONFIDENTIAL TREATMENT REQUEST, AND HAVE BEEN OMITTED FROM THIS EXHIBIT. COMPLETE, UNREDACTED COPIES OF THIS EXHIBIT HAVE BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION AS PART OF THIS COMPANY’S CONFIDENTIAL TREATMENT REQUEST.

KCP-4504921-5

NOTE: PORTIONS OF THIS EXHIBIT INDICATED BY “[****]” ARE SUBJECT TO A CONFIDENTIAL TREATMENT REQUEST, AND HAVE BEEN OMITTED FROM THIS EXHIBIT. COMPLETE, UNREDACTED COPIES OF THIS EXHIBIT HAVE BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION AS PART OF THIS COMPANY’S CONFIDENTIAL TREATMENT REQUEST.

Exhibit A

Existing Vendors

KCP-4504921-5