My parents just bought a Formula f-180 and apparently when the boat was redone 3 years ago, the guy removed the bow cleat and glassed and painted over the hole. He installed some Attwood pull up cleats at the stern only. They ordered the same kind and want me to install them, but I dont know what material is best for the backing plates. Should I use 1/2 marine plywood or can I use 1/4 or 3/8 aluminum? Here are the cleats I am installing.

I would use some 1/4 inch aluminum plate. That is what has been on all of my cleats on the Pantera and AT.

Aluminum plate, 1/4" or 3/8" should do the trick.

Should I glass it or epoxy it to the underside of the deck?

Just some caulk under the base plate at the studs is all we ever do with all the deck hardware.

Like he said. maybe just some caulk to hold it in place. You don't really need to secure it. The bolts will do that.