I can understand your concerns Larry but this design as been well proven. Check out the link below and that will show you one company that uses the pinch seams. in fact, this was the company I went with for my Cherokee and I bounced my cherokee off some boulders hard, came down on them hard and all that ever happened was the paint was scratched off the sliders and that was when I was out crawling on rocks.
The picture that shows the frame bushing mounts are for reference of the bushing only and nothing else, that is not my pic. the way that person has his mounted it could cram up into the body. He is only using two points of mounting on the body. Best analogy is think of the bed of nails thing. lay on one nail and its going through ya lay on hundreds and you wont go through.
Yes what I am calling the pinch seam is the pinch seam you are thinking of like the Protofab sliders (in the link below) with a 1" bars spanning the length of the pinch seam and being bolted up like that you are distributing the impact amongst 7ft instead of just 4 or 6 bolts like most people do at the body mount trusses like you see in that guys pic. In that case all the impact psi is going to starting banging on those two spots instead of the full spread.
http://www.protofab4x4.com/products.php?ID=00&ID2=9