Epoxy

Dans, I don't believe that CC ever sealed any of the ply they used for the seats or coaming. The coaming because it sits vertical and the vinyl is wrapped around the bottom edge would trap water and wick into the ply. The seat ply may be protected more with the foam and/or drain the water better. It's good that you are sealing them but the polyester may be overkill. Like I said, any wood sealer will work for this and would be allot cheaper.

Most boats are constructed using polyester resin in the fibergla$$ construction. It will work fine for sealing the wood. Make sure you use plenty on the edges as it will soak in readily.

I like to construct seat bases from treated plywood as wood quality is really not an issue since it is totally covered. Coaming pads see very little water and thus usually are never much an issue.

For the seats and combing pad plywood just about any sealer will work to keep it from absorbing lots of water. Polyester is hygroscopic so I wouln't use it in the bilge for the stringers since it will keep the would damp. Epoxy is the way to go there. The 100% waterproof statement on the can refers to the polyester not being affected by water and breaking down or dissolving like a non-waterproof glue will.

Just cut new wood for seats & combing pads out or regular plywood.Do you guys think "evercoat boatyard" brand polyester resin will do the job to seal the wood.Would not use it on my floor ,but was wondering about seats.Thanks,Dan