if you're still going to use plywood - anywhere in the boat - give it a coat of thinned out resin especially if you're using poly resin. It'll soak into the wood deeper providing better water resistance, and if you can get the next coat with glass on before the thinned coat dries even better adhesion. There are products made specifically for thinning resin, I believe acetone works too but check that first. I've had plywood decks last 20 years, key is sealing up any screw holes, over drill, fill w/resin, then re-drill.
you can get composite materials for not much more $$$ than plywood, on a boat this small it's not much of a price difference. just sayin. I use a little of both now.
