We used 5/8" Coosa on the cockpit hatches of our Bertram. The only place around me that carried it was Hamilton Marine in Portland ME. The price was crazy then and it's gone up in price if my memory serves me correctly.
https://shop.hamiltonmarine.com/prod...-26-43605.html
I would consider a quality plywood and epoxy- seal the crap out of it.
I was disappointed in the fact the Coosa wouldn't hold a screw over time.