Thank you slocum2. I was wondering why Cal had sandwiched plywood between two layers of fiberglass with no way for water to dissipate. Your idea of the larger holes filled with epoxy answers the question of how to keep the water from contacting the plywood in the first place. Even if the screw hole leaks, the water will travel into the cabin and not make contact with the plywood. Brilliant!
I'm headed to the boat to start work!