I used an excellent stripper called BIX from Home Depot. Spray on thick, let sit maybe 10-15 min., spray a little more, wait 5 min, then run over it with with a plastic putty knife/scraper - Like butter! Then I hit it again later with a light coat and wiped it clean to the gelcoat. That will get it good enough to put another clean coat on. Get the BIX that says ok for fiberglass.