I purchased the truck in my signature a couple of weeks ago and it came with the cap. It is an 08 so my assumption is the cap is 3+ years old. I went up top to remove the foam the previous owner had put on the Thule bars. Up there I notice a ton of minor cracks and a few larger cracks in a circle patter near the rear corners. Some look like minor surface paint cracks where others you can tell they are about 1/8" deep. Looks like weather stress or something, unless it was heavily loaded? Anyone else have these problems? The sides are fine with no issues. I will try to get some pictures up tomorrow.
My friend has a Leer camper shell on his 2006 F250 Powerstroke. He offroaded the truck as if it were a Raptor. I've seen him keep up with motocross bikes in the Mojave and catch two feet of air under his front tires.
He actually managed to expel battery fluid onto the bottom of the hood and tweek the bed out of alignment. The Leer camper shell was completely undamaged. I'm guessing whatever was loaded on the top of your shell caused the cracks.
I have a SnugTop shell and I seem to recall the company mentioning roof loads on their website. I do know not all camper shells are reinforced to take a roof load.
Sorry the pictures are showing cracks in a circular shape. There is too much reflection of the sky in the paint throwing off the pic. The actual fiberglass below looks fine but I've head there is a gel coat that goes on top of the fiberglass to make it smooth and paintable. That is was looks like is cracking.