Hi,
It probably is an issue with Mold, especially in Florida. The Charcoal Filter is overkill on a convertible - not worth the money unless the Top is up 90%+ of the time.
Check drain tubes as has been suggested and also recommend using an anti-mold/mildew spray such as:
http://www.healthgoods.com/Shopping/Allergen_Control_Products/Allersearch_ADMS.asp or
http://www.drugstore.com/products/prod.asp?pid=80724&catid=22978&aid=335972&aparam=mite_nix_organic_anti_all . Remove Filter, start car andf run AC Unit and Fan. Liberally Spray either cleaner into the intake. Suggest respraying every week until smell is gone. Hope this helps...
Happy Motoring!... Jim'99
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