: My logic at the time went something like "I'll slather on some epoxy to
: seal it, and get a the beauty and thickness of this wood for cheap."

I did one boat of cheap 4 mm birch plywood, used epoxy to seal it and have not had major problems so far after 3 years. I had a scratch at the bottom that penetrated the fiberglass and caused minor water damage but that was fixed easily and is not abnormal. Seal every S&G hole with epoxy putty (OSH) because they absorb a lot of epoxy that will degrade the seal. Can't help you with other types of sealants. You don't need to apply lots of extra epoxy, just seal with extra care.

Henk