[wingnut60]

Not really a Thor problem, but an overall design deficiency. Many units travel without any cap separation, but lots have the problem...1/32" sheet metal just does not have enough thickness to keep the screw threads engaged, thus many of them back out. If you have the problem, you can actually see the cap move in the rear-view mirror as you travel. Needs backing of some sort for the screws to tighten to.
I had Rolling Retreats work on mine--looked/worked well for maybe a 1000 miles of movement, then one screw on each side began backing out again. Used JB Weld on the screw threads, seemed to hold. But traded it off for a MH before enough traveling to see if it was permanent.