I put my sleeping pad at the bottom of my Carradice camper and it gives enough structure. Also I fill it tightly with other stuff like tent and sleeping bag so there would be no chance of it sagging if I used a rack....but ideally a Carradice saddlebag is best used without a rack so the weight is tight up underneath the seat. Filling the bag tightly for structure is also a good reason to get the long flap so if you do need to carry some extra groceries you can do that without reducing the rigidity of the saddlebag.