When I had the problem with the badly fitted hatch, I used West System epoxy to seal the bare wood edges. It's about £30 for a litre, but will last you for ages if you keep it cool but don't let it freeze. The West Epoxy is thin & penetrates the wood nicely. I'd then add some colloidal sillica to an epoxy mix, this turns the epoxy into a thick putty which is great for sealing holes etc. Ordinary epoxy (aralidite e.g) warns against use in permanently wet situations, West is designed exactly for marine applications.
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5