Newbie glassing over a thru-hull
Greetings to all. I want to fill in 2 un-used corroded through-hulls in my boat (fiberglass), It's my first time doing fiberglassing and I've been reading 'hull and deck repair' by don casey (any other good books on it you guys can recommend?), but have a few questions I would like to ask. They're both below the waterline and about 3-4 inches diameter. I don't care much for looks, just strength.
The idea then, is that I have some kind of plastic backing plate on the outside of the hull, put a bit of gelcoat down first, then glass on top of that.
I would like to use epoxy if possible, just because the book said its stronger. Can I still use epoxy if I'm putting a layer of gelcoat down first, or should I just use polyester resin? Or can I use something other than gelcoat for the outside layer, like just pure epoxy or paint?
And secondly, how do I stop the epoxy/resin/gelcoat bonding to the plastic backing plate?
Thanks in advance