I'll second the advantec sheeting. Their whole advertisement campaign was related to water shedding. I extended a deck on a small fiberglass boat one time using it. It was a little thick but felt very sturdy after construction. I covered mine in outdoor carpet and used really good glue from the carpet place. Cant remember the name of it but u brushed it on both surfaces, allowed to get tacky, then put on. I carpeted my deck before I put it into my boat then wiggled it in place. Might not work for ur purposes but the fit and finish looked as god as factory IMO. When I sold it the guy that bought it jumped up and down on the deck to test it and said "not only does it look great, its strong"