You can use a number of different things to clean fiberglass. Stuff that you'd use in a fiberglass shower stall in your home, for instance. 409, Tilex, cleaners with bleach, Awesome (from the Dollar Store), Magic Eraser, and on and on. Once clean apply a really good wax like Meguires.
Ten Forward - 2014 Escape 5.0 TA
Double Yolk - 1988 16' Scamp Deluxe