If you want to make your life easier about the messy fiberglass you can always use the cloth medical tape (like what you would tape your ankles with in sports). Thats what I did. 0 mess, clean, and easy. Check out my armor progress thread for some pics of it.
You can use fabrics like spandex. Many custom speaker boxes you see in these magazines are molded in fiberglass over spandex. Thick pantyhose works just as good.