Curious of your plan of attack. Are you planning on filling in the entire hole and then re-cutting for the new intake? Have you laid in the berk intake to see exactly how much and where you need to add or remove? I would think you'll be working from both sides (top and bottom) of the hull, which means flipping the boat. Best way I can think of is to make a template or mold of what you want to add. I would use a polyurethane laminating resin for sure, not epoxy, and the bi-axial or heavy mat like Jake said, it's what your hull is made of now. I would think a gallon would be plenty and maybe a yard or yard and 1/2 of clothe if you don't waste it. Are you closing in the transom any?