Standard paint stripper will eat the fiberglass in a heartbeat! The best thing is Easy Off Oven Cleaner, Heavy Duty. Check the ingredients, as this is the only brand and style that comes with lye. Work outdoors; spray on, let it bubble, and then wash off with a hose. Best applied with temperatures above 70*. It is absolutely great on fiberglass, chrome, and other metals. If the paint is really hard to come off, use a stiff bristle brush to help the Easy Off do its thing.
Oh...and wear gloves!