You need to see where the lowest point on the rear portion of the unit is----the bumper may clear, but things like spare tires underneath, rear stabilizers, auto levelers, and black/gray tank outlets may be the lowest point that will bottom out on a slope.
It's a limiting factor for me. I tried 4 different fivers before I found the one that would make it up the driveway. If you are working with a local dealer, make that a condition of sale----it has to be able to make it up the driveway.