You would use the same product recommended for, or safe for fiberglass/filon. All the Azdel amounts to is the substrate underneath used in place of an outer layer of luan plywood. I would assume your fiberglass is a product called Lamilux.
Azdel = great marketing word...will not rot like luan but will still delaminate from the foam or fiberglass if you get water in the wall the same as anything else.
As you should and not be lured into a false sense of security that azdel is this revolutionary solve all problem material that marketing will lead you to believe. If you slack on your maintenance and get water in your wall that azdel
Ok So I am off with my trusty Goo Be Gone!
Hopefully remove these super ugly Dealer Stickers!!!