Here's another thought ... I drive a 3500 duly. Even when the topper is NOT on the truck, I still have to climb into the bed, via the tailgate, to get anything out of the front of the bed. The sides are just too high to reach over, and with fat dual fenders, it even more impossible to reach over. So actually, there's no difference between crawling in the bed with no topper and crawling in the bed with a topper.
If you have a duly, especially with the higher sided bed rails like the newer trucks come with, accessing from the ground along the side is just about impossible. So those flat covers are really no advantage. And actually, I would think removing them, or folding them back would be difficult too, because you've got to either climb up on the tail gate to get started or use a ladder from the ground. Those fat fenders just make accessing the bed, or the side of the truck difficult, if not impossible.
That's another reason for the side tool boxes that work so well. By the way, my last truck... the shell was never removed until I sold it. My current truck, I've taken it off twice ... only to get the bed liner sprayed and the second time when I had to get the fat fender fixed because I got a dent in it.
If I need height for hauling something, I have a 6 x 10 bed utility trailer. If I really need the height in the bed of the truck, I can take the shell off. On a 3500 duly, the weight of the shell is insignificant.
Just my 2 cents worth of thought here.