Please, you are all over thinking this whole thing. I have a 2018 3901 and this has always been a problem from day one. There are two sets of bars that hold the mattress in place, one set at the top and one at the bottom, when the bed is raised the ones on top force the mattress down and so all you need to do is have your partner stand at the base of the bed and hold it in place wile you raise the mattress up, not a big deal. it is part of our standard routine.
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