Oak and other hardwoods should really use Epoxy because Poly doesn't stick real well to oily woods, but you should never use Epoxy on a fiberglass boat. Vinyl-Ester has the properties of epoxy and the same solids. Resins and Gel-coats are all about chemistry. The biggest problem is the people that sell this stuff don't really know what they're selling. Poly won't stick to Epoxy, and gel-coat is poly, I think Vinyl sticks to everything. Instead of following what the manufacturer did, people want to "Improve" things and only make them worse. I don't care what you do to your boat, just don't use interior grade plywood, it's glued together with a water based glue, or PT because it warps, and poly won't stick to it, and always use Polyester, or Vinyl-Ester (or a mix) resin.