RE: fiberglass covering question-blisters in sun
I've built two small sailboats and reglassed many hull repair sections. Blistering is caused by one of two things: improperly mixed/cured resin and moisture intrusion. The latter takes years to appear, so I am guessing the former. Be sure when you mix either epoxy or polyester resins to mix very well and then allow them to sit and link before applying them. How long depends on the cure rate of the hardener you are using. If you mix fast and apply immediately you can get places in the suspension where the hardner is thin or absent. These take days, weeks or years to harden.
Sunlight warms the uncured resins unevenly, the darker areas increased the temperature difference. As a rule of thumb you should not work in direct sun with paint, glues, waxes, dyes, stains or epoxies where it can be avoided. It's just one more thing you can't control.
When you step aboard a new boat and get that "new bost smell" . . . that's uncured resins. It can take months to fully set.