Just a thought; Lippert makes frames for many RV manufactures, but to the individual specifications written by the RV manufacturer. If the RV manufacturer has said that the frame can not withstand the stresses of a leveling system, I would be inclined to listen to them. If Keystone says no, but Lippert says yes, who will be honoring the warranty on your RV if there are issues? Lippert, I think not.
Our Big Foot system allows you to raise a single leg, but recommends doing a pair at a time to prevent undo stress. Since the RV manufacturer cannot control how the levelling system will be used, they of course, are taking the conservative approach.
During a normal setup, the Big Foot first lowers the front legs and then adjusts the fronts to acheive side to side level. It then lowers the rears to achieve front-to-back level , and then each rear leg to get the back level side to side. In that process, it is adjusting one leg at a time. Even this minor torquing to the frame imposes stress that the RV manufacturer may not feel that the frame is able to tolerate.
Stuart, Lynn, Robbie and Abby
2012 102-F41RLTSS New Horizons Majestic
2013 F550 Super Duty w/Utility Bodywerks hauler body