Pop up vs hard side loading

I'm curious what you mean by really unstable. IMHO, no camper with the jacks extended to loading height is going to feel stable. Those spindly jack legs are going to flex a little when extended. That doesn't mean the camper instability is unsafe, but it's only meant to be in that condition long enough to get the truck under, or out from under the camper. Once off the truck you should either lower the jacks all the way or place some support under the camper tub if you prefer to not have to raise and lower the camper all the way from ground level to loading height and back.

I'm not familiar with hydraulic jacks, but once you get the camper on the truck and the weight off the jacks, check just how rigid they are. If you're getting a lot of flexing/wobble, maybe think of replacing the jacks instead of the whole camper.