That is very doable, and fiberglass is super easy to work with. Use a higher quality fiberglass resin, not the Bondo stuff from you local auto parts store. You can use metal straps and pop rivets to temporarily hold everything in place until you get enough resin and cloth on it to hold it. Then remove the metal strips and rivets and glass over everything. Do not be afraid to really grind on the existing glass and go well beyond your joint with it. You must provide a superior surface on both sides of the body for the new resin to bond to. An ideal situation would be if you could actually find out what brand of resin the body manufacturer uses. You will need a good supply of heavy weight mat, cloth and resin.