I've thought about it before. The (normal) snorkel matches the curve of the body and rests on the flare, to make it work with fiberglass you would have to cut the fiberglass so the snorkel would sit partially inside the fender and partially outside. You could do it pretty easily, it might look a little weird since it'd be a half exposed tube more or less... I've never seen any pictures though of glass + snorkel.