Correct way to fill in a thru hull hole

[Normagain]

I'd definitely go with epoxy resin in that application. It will be a much stronger bond and repair. My first boat was a 17' Whaler where someone patched a 2' X 4' section on the bottom of the hull where they had run aground. I didn't know this until one day the entire patch came off while coming in from a day's fishing. It wasn't pretty looking but the foamed hull saved me. I'm sure you could do it right, but no structural polyester repairs on the hull bottom for me.