I have a couple of Starcrafts from the 60's, they have the original transom wood, one had a plywood floor placed in it at some time in the late 60's, because the wood was of a decent grade and left open, it lasted for 3 -4 decades with zero attention. Now if you cover it with carpet, vinyl, or something else like a mound of wet leaves while sitting in the side yard, the lifespan is shortened dramatically. Products like spar varnish, paint, Thompson's Water Seal, etc, are not going to extend the lifespan much once carpet is laid over it, epoxy is the only product that will extend the life of the wood, and only if you don't drill holes in it and leave them unsealed.
My boats were stored outside on the beach, but upside down most of the time, so the plywood was dry except when it was being used. Plywood is cheap and easy to replace, so I don't do much of anything to protect it on an aluminum boat, at most I'll use some porch paint and grit to make a non skid surface if needed.
These boats were used like tools, checking crab pots, fishing, shrimping, shuttling to larger boats that were kept tied to buoys all summer, etc, we did nothing to make them look better, this allowed the wood to survive longer.
