[warthog5]

Here's the thing about adding glass to Fir plywood unstead of just a couple of coat's of epoxy.

Fir plywood is what you would generaly buy as Marine plywood.
It's also lighter than Pine plywood.

If you don't add the glass the wood will still check and open up.

I have a long term experiment project that proves this well.
It doesn't take much glass. 4oz cloth will stop it.