I have had no issues with mine on my '01 Dodge dually with the stock setup. However I have read of some trucks, newer ones, that have a problem with the hitch denting the bed. Since it doesn't seem to be a problem with the older trucks, I think there may an issue with the newer frames or bed material.
Most of the weight of the 5th wheel is carried by the hitch pin, just like a gooseneck. IMO if you have movement of the hitch base causing denting of the bed then there is a problem with the hitch mounting hardware or the frame itself. Just what I think anyway.
But it is a wonderful hitch, I've had mine for about 8 years and still love it.