There is no glass over plywood in the Tom Cat- Some of the laminated cabin ate materials in the "furniture" interior are a plywood, with a laminate exterior, but not structural.
The penetrating epoxies have very limited use in the C Dory (and only occasional use in other boats).
If one uses plywood and then glasses over with polyester resin, this is not a very good construction technique. Plywood, with epoxy and glass is a far better technique.
As for screws and cored structure--use a Dremel tool and remove the core in an area where you have drilled a hole for a screw, undercut the glass, and then fill the hole and under cut area with thickened epoxy--then re-drill the pilot hole and put the screw into the epoxy, with sealant.