http://www.dicor.com for complete maintenance info on rubber RV roofs.
Some units have a full 3/4" plywood base under the membrane and substrate. Those are what's known as a "walk around roof." Others have 1/4" luan. If it has the thinner material, you should be able to press down halfway between the roof joists and see some flexing. The 3/4" won't flex.
The roof joists themselves are pretty strong. If you throw down an old blanket and then a piece of 5/8" plywood that is long enough to span a couple of joists, you can generally get up there safely. Walk only on the portion of the plywood between the joists.
Weight limit? I don't know for sure. That's a question for the dealer or Keystone, I think.
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'11 Cougar 326MKS loaded with mods
'12 Ford F250 SuperCab 6.7 PowerStroke Diesel
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