Trailers with solid metal deck/platform

Hello..newbie in CA here with first time build. I am considering a used trailer as a basis for my benroy build and it has a complete deck made of diamond plate & painted on it already. I was thinking this would be a good way to go but wondering about the fact that diamond plate isn't a 100% flat surface. Therefore how to assure the plywood bolted to this deck could be sealed properly to avoid moisture getting in between the plywood & the deck or if I really had to be concerned at all. Anyone have experience with building off an existing metal deck like that?