VeroWing
GreatGrady Captain
I've done several with marine plywood and in a few years they started showing water intrusion on bottoms. On my last one (22 Seafarer) I used this pfc board, and it was cheap, weatherproof, easy to work with, and lasted years until I sold boat, and I'm confident it still is. The cabin bulkhead is not a structural wall, just a divider between cabin and helm.
Veranda 1/2in. x 48 in. x 8 ft. White Reversible PVC Sheet H120AWS6 - The Home Depot
Prevent dents and weather damage to your home with this Veranda HP White PVC Trim. Perfect for windows and siding, this lightweight, solid board offers water, mold and mildew resistance. Fire-retardant
www.homedepot.com