i have a 1989 seaswirl 19' sierra cuddy classic. when i bought it it was outfitted with a bait tank with water drawn through the floor of the boat under the engine. it has a thru hull fitting. i would like to get rid of the fitting and patch the hole. i have done some fiberglass work before and it is not a hard thing to do. But i need advice from an expert.Do i patch from inside or underneath? thanks for your time..