The primary motivator for this was to relocate some of the weight from the forward end of the pop-top. In years past, I've overloaded the front end a little bit by putting the slide-out solar panel and recovery mats on the forward rack. My original goal was to make these things easy to reach by standing in the open forward door area, but the side effect was that raising the pop-top was significantly harder, due to the extra weight way out on the long lever arm of the hinges/top.
Relocating the TRED Pro recovery mats is step one to remedying this. As a nice bonus, the mats are now even easier to access, without the precarious standing-on-tip-toes, reaching over the awning housing, from the passenger door. I may also eventually take the hit to solar efficiency and move the solar panel aft on the roof, closer to the roof rack. The math says I may even be able to add a second panel with a net decrease in roof-lifting-effort, just because the lever arm will be shorter, even with extra weight.
Then I moved onto steel. This bracket connects to two of the holes that go through the roof for the pop-top hinge on the drivers side. These are secured into a thick backing plate with tapped holes that is bonded to the roof on the inside.
The arms protrude out from the body, and are connected by another piece of L-track. I couldn't use RivNuts here because there's a second piece of sheet metal at an angle behind the outer skin here (from where the "wall" and "roof" panels were joined at the factory) - so it would have been hard to get a clean seat on the nuts. (I'm glad I suspected this would be the case and eventually double-checked by drilling holes on a junkyard van body.)
The top and bottom bits of L-track are then tied together with a couple of lengths of 3" x 1/2" aluminum C-channel, fastened to the L-track with mounting studs. This makes the rack very rigid, but lightweight.
Next comes accessory mounting. You can see that the hold-downs for the recovery mats are 5/16" stainless eye bolts. I used a pair of nuts to jam a fender washer at just the right depth along the bolt threads so that they tightly hold the mat to the rack without protruding too far through the back of the C-channel. (The eye-bolts are threaded into aluminum RivNuts seated strategically into the channel material. I could have used the supplied TRED mounting plate that gives you a pair of protruding "studs" to mount the mats on, but then there'd be these two aluminum studs sticking out of the side of the van (at head/face height, no less), all the time. I wanted this to sit fairly close to the van when I don't have the mats mounted.
For the ever-useful shovel, I just relocated the Quickfist clamps I had originally mounted on the roof rack. It's nice to not have to try to stand on the rear tire to get my shovel down anymore! Obviously I have a bit of real estate left, should I need to mount another tool.