Ummm... you've been dealing with some pretty crappy fiberglass then.
A three-layer weave is extremely strong. Most of the "fiberglass-hatin'" that you hear on this website is from people talking about lower fascias and such being built out of fiberglass on a lowered car, and the glass breaks after they hit curbs and speedbumps.
Fiberglass, if laid properly, is extremely strong, and has enough give that it won't break. Keep in mind that boats, aircraft, and Corvettes all have fiberglass and resin gelcoat panels, not to mention Cobra S/C and other kit vehicles. If it works on them...
For an interior function Panther, glass will work fine. Take your time and make sure the bubbles are out and each layer of glass weave is at a 45 degree angle to the previous layer. Mix 1/2 Bondo and 1/2 resin and spread over the final layer, you can sand it like regular body filler.
Actually, I'm planning a one-off glass bumper on the rear of the next car.
