This lack of info on the matter is probably due to the difficulty in determining weight limits. With weight are you hauling 8' or 12' 2x4's? the 8's won't move much but the 12's will flop and bend up and down thus increasing stresses. How many people out there will misunderstand the difference between dynamic and static loads? How many people do you know that can accurately calculate a dynamic load on a truck? Also how you mount your rack on top makes a difference, are you using 4 bolts or 8? 2 bars or 3? Would you put into writing what the load limits are knowing how "sue happy" people are in the US?
That said I have an ARE topper, Yakima tracks added, a Camping Lab RTT mounted when camping. I only have a few trips out with it so far, but no cracks or damage are evident.
However, this is not my final setup. The truck came with the topper when I bought it. Eventually I will build a rack for the back that puts the RTT ~4-6" above the height of the cab. In order to decrease drag while trying to maximize avail space in the bed. I'm also doing this for visibility. My truck is and will likely be used for DD purposes for the life of it. And I really hate not being able to see out the back while driving in heavy traffic and in parking lots. I don't wanna miss a car flying up or a kid walking behind me.