Once the fiberglass (or the roof paint) begins to chalk, the only permanent solution is to re-paint it. Dicor makes a Fiberglass Roof Coat (paint) that works well, though it is pricey. You could also use a marine deck paint or an automotive paint, anything intended for exterior use in full sun. Just clean & prep the surface and paint. I did mine in about 6 hours, including a second coat.
Former owner of 2004 American Tradition
Home is in the Ocala Nat'l Forest near Ocala, FL