Ok campers, I got the shelf in and the wife and I love it. Here's the finished product loaded up.
To start with I located my d-ring hooks far enough down from the roof peak so as not to be a problem when the roof is collapsed flat. As you can see they are slightly below the locking levers for the side. Additionally, I placed the a bit over 4" from the wall and the second one an additional12" from the first. My shelf is 12" deep.
To attach the d-rings I cut some 1/8" x 2" steel flat stock into 3" plates, drilled, sanded, primed, and painted to match on the outside of the roof. I used 1/4" x 2" stainless steel screws and nuts and a generous coating of silicone caulk between the plates and roof.
Looking back on it I wish I'd mounted the d-ring 90° from current. Would be easier to attach the type of clips I chose. I attached, with zip ties, a round ridged curtain rod, painted white, to the back of the closet shelving to keep the shelf from sagging. I used sturdy clips to attach the shelf first to the rear d-ring then to the front.
Once the shelf is hung I suspend wire hanging baskets from the shelf. You might also notice I now have a place to mount my paper towel holder.