George,
I think this might be the PVC shelter thread you're looking for:
http://www.keystoneforums.com/forums...highlight=tarp The member that built that structure was last on the forum around mid December 2018, so a bit over a year ago. He may not respond to any comments, then he may.....
As for walking on the roof, there's a current thread where a member discovered his roof "crushed" after maintenance was done by a dealership. It happens, maybe not as a direct result of walking on it (he's not sure what damaged his roof) but the repair is still "just as expensive and just as difficult" regardless of whether it's a result of "walking on the roof", "stepping in the wrong place" or "being a larger mass than designed" being applied to the roof.....
http://www.keystoneforums.com/forums...ht=repair+roof There are photos of his "rafter network" and the damage done to a rafter.
Although Keystone uses several different types of rafters and thickness of roof decking on trailers in different price ranges, essentially the "basic construction" (rafters, OSB overlayment, TPO membrane) is the same on all Keystone products.