Re: subfloors replacement - aspenite ok?
If you don't want to use marine plywood, just get some pressure treated or exterior plywood. If you use PT, let it dry for a few weeks before you use it. It will want to warp as it dries. One poster here screwed his to his garage wall while it dried. I think that's an excellent idea. Either way, seal all sides and edges with resin. Use at least 2 coats as the wood will soak up the first coat. Cut it out as accurately as possible or you'll waste a lot of resin filling the gaps at the edges, btdt. BTW, the chemicals in PT will eat certain types of screws over time.
I'm afraid that aspenite (OSB) will just fall apart.