Gelcoat cracks because the laminate underneath is flexing and/or it's bent around too tight a radius. If the gel coat is applied too thickly, very little flex will cause it to crack. If the gelcoat application is proper thickness, takes more pronounced flexing to cause it to crack.
Our Westsail 32 must have been laid up on a cold day in SoCal (February). Apparently the applicator kept spraying on the gel coat to cover the vertical surfaces as it ran down oand built up on the horizontal surfaces. The cabin
top and walkways turned into a mass of cracks after a couple of years of cruising. Tried reaming out the cracks and filling with thickened epoxy but the cracks kept coming. Finally had to grind off the gelcoat on those surfaces to cure the problem. Used a Sander/Polisher with max 3000 rpm
and an 8" foam pad and 100 grit sand paper. Messy work but the low rpm
of the polisher made it easy to control and didn't melt the surface like a high speed grinder will. The foam pad's flexible surface kept me from gouging into the laminate. Painted the decks with epoxy primer and 2 part paint. Still looks good after 15 years.
If the problem is caused by flexing of the laminate and/or tight radius joining surfaces, My painter said to just use a quality epoxy primer without grinding out the cracks. The primer is flexible and fills the small cracks and imperfections and won't reveal moderate cracks underneath. The two part polyurethane
paint coating is very thin and flexible so not prone to repeating the cracking. If you want to be absolutely certain no cracks will print through, scrape or grind out the cracks and fill with epoxy. The guys who sprayed my boat used AwlGrip epoxy primer but another manufacturers LPU top coat. They said the primer is the key to a great looking, long lasting finish. Of course you have to sand the primer. A year later, none of the areas with cracks has come back