Re: trailer
your water question is only relevant if the spot is below the water line...is it?
secondly, like most guys here, I have never seen a roller rub down gelgoat and eventually fiberglass unless there was a roller issue that caused it. the only other thing I can think of is if when you put the boat on and off the trailer, you maybe were not centered properly and the boat sat odd on one of the rollers..??? that would certainly put more pressure on one spot than evenly across the 30 or so rollers you might have..
if the break is down to fiberglass and its lower that the rest, my opinion is that roller, for whatever reason is excerting more pressure on that spot...the bigger question is why? again, is the boat centered and on the trailer properly? is it kicked or leaning in one direction?..are the swivels on the rest of the trailer stuck so the boat is leaned?..etc..
I would determine if the break is above or below the water line..then act accordingly.. patch or, if accessible from the inside see if its come through, if any water is already present...