We had axle problems two years ago. Lippert came 500 miles, to where we were to change out an axle (both had just been changed by Lippert from 7M to 8M#), so we could get back to their service center to replace them again, this happen on two separate times within one month. They used our LevelUp 6 jack system both times to completely raise our 5th wheel off the ground (it scales at 18,300) and work under it. These guys were Lippert employees!!! Also at their service center in Goshen, IN, again, they used the LevelUp to raise the 5th wheel completely off the ground and worked under it. Their answer, the jacks fully retracted still leave 12-18" of clearance under the 5th wheel and 4-6" or more under wheel hubs. But, it is impossible to have a complete failure of the system were all 6 jacks retract all at once, and IF they did, they would just stop at the bottom, not "bounce" lower then return up a little. They also said, if someone was concerned about a complete failure, use car stands beside each jack, equal to the 7,000#'s of the jack capacity. We have used our LevelUp many times to lift it completely off the ground. Where we are at present, because of health reasons, have had to be in the same place since middle of April 2014, with one side off the ground and it has not move at all, (because of the slop of the ground I cannot get both sides off the ground). But, I have measured and have markings on it to check if it does, it has not. Since 2012 when we had the LevelUp installed by Lippert, just for "grins and giggles" I have set up a different places for 3-6 months and have raised the unit completely off the ground, (never did any work under it but I would have if I had too). But, nothing move, had measurements and markings to check, plus, less movement in the 5th wheel.
So I say all that to say, I personally would not hesitate at all, to lift it completely off the ground for any reason, long or short term. Both by the experience I have seen, and what the employees of the manufacturer of the system do at their service center and on the road. When our unit was there, there were "many" bosses, from operations, engineering, production plants, etc, all looking at what happened causing the problems with our 5th wheel axle's, while it was completely off the ground, and nothing was said about it being off the ground, and with no other "emergency" support system. Like stated in an earlier post, the "warning" is a disclaimer for Lippert. Like the 30 some "warnings" on any ladder. LOL
But everyone has to make their own choice. Everyone has seen someone else do stupid stuff with car jacks, bottle jacks and floor jacks. But this system is nothing like those, kinda like comparing raisins and oranges. :B
Hope this helps and God bless,
Mike