Scarry. at least what Im reading..
While stationary jack extensions sounds like a good idea as far as not having to raise & lower the camper jacks as far and still drive in/out... creating 4 independant 'pedestals' that are taller than base (3' ?), your setting up potential disaster. I suppose you could tie sides together-possibly across the back and still drive in/out, attach something across front after moving truck. Better/safer would be other ideas mentioned, after moving truck put something under camper at raised bed height to stabalize, X boxes, sawhorses, pallets even etc.