..Putting a spare wheel on the outside surface at the rear of F.G shell without reinforcement from the INSIDE is ...playing a dangerous game on the road, in my opinion. As I know of, 18wheeler manufacturers who have their roof cabin made of fiberglass. When install a satellite bracket in the back of the roof which is so
light compared to a spare wheel of trailer campers, they do install a square piece of aluminum as reinforcement from inside. I would do the same when coming up reinforcement my bunkbed at the hinges. A spare wheel is too heavy for fiberglass shell and with the combination of vibration on the road, I would think it is dangerous without reinforcement from inside of the shell. Just my thought...