I had a leak in my front hatch last year. Mine was leaking under the frame and not from the gasket. Luckily the core was dry since it was dripping down between the frame and inside trim piece. The PO has removed the frame and put some silicone between the trim piece and coring. An extra 1hr of work he could of sealed the core for good. So I recommend coring out all around the hatch and not just the screw holes with epoxy or resin. I found this dremel cutting tool very helpful. Run the shaft along the fiberglass using it as kind jig. It will cut out about an 1/8″ just enough to seal the core.
Taping a sheet of plastic on the inside will catch the coring and drips from the epoxy. Also it would be a good time to paint the inside trim piece, I found