Subj says it, actually
I have been thinking about the issue all night, though (yes, I've got nothing better to do). It seems amazing to me that bare gelcoat would be so succeptible to water damage. Someone should have noticed? Or is it that no one out there has boats sitting unpainted in the water for extended periods?
For clean experiment (and to help me decide what to do), I will remove all paint from the same area on the other side and compare gelcoat condition. I'll post pictures here if anyone is interested.
The only two I've dealt with are both up here in Massachusetts, so likely not useful for you. It would help if you said what geographic area your boat is in.