I have a 78, 24ft Argosy that had a hole in the sink in that rear bath. You can't get to much in ours and you can't even change out the faucet without taking the whole sink structure out. We used fiberglass and then bondo, sanded it down and then painted the whole sink. It looks great and you can't even see the patch. I've used just almond colored caulk to fix discolorations and cigarette burns and then lightly sanded over them. It works well. I've also used the caulk method on our 76 Sovereign
and it blends well. Just shop around for the right color caulk. There are so many off white ones. I just get the kitchen/tub type in the squeese tube. No problems so far.