The subject is a 74 20 cc with some problems

[optiguy]

Any good lumber yard should be able to order marine grade plywood. Don't use any other type of plywood as the glues used to make it are not as strong. Also the quality of the plys and void content is better. As far as the resin "biting into the wood better", that's not really true.
Most failures can be attributed to improper use and application. I can go on about this for hours after 30+ years of boat building and repairing. If you have any specific questions, just ask.
Bill