Couple things when unloading on a slope in any direction, it's way easier to load it back up if you take note of the angles both directions (and height). Then you can preset the camper to exactly how the truck will be.
I don't worry about shimming the Jack pads level unless over 3? Deg. Otherwise, yeah if you know your going to be on significant slopes if just bring some shims. Don't need to be wedges. Good plywood pads and then some 2x4s blocks to level the pads up.
Bottom line is (within reason) as long as it isn't too steep that sliding is a concern, if the pads are level you're fine.