The site is designed for manufacturers of fiberglass vehicles and sports equipment ... but the Valspar site has a great gel coat troubleshooting and repair guide.
Might be a starting point for some of you, restoring older trailers.
Interesting reading for the rest of us.
The hot link is to the troubleshooting page.
To access the gel coat repair area, you have to click on the gel coat repair button near the top center.