I've lived in my camper for up to half a day off the truck while getting brakes serviced. You just drive out from under the camper and then lower it to a few inches off the ground, and it's pretty stable. My jacks have "danger" marks showing how far they should be extended when the camper is on the ground. These campers are indeed designed to be used off the truck if you want to/need to. I don't feel like it's super-stable, though, especially in high winds I've experienced in the desert. Plus, I can't think of a single good reason to ever really drop the camper except if you literally have to (i.e., need to address a mechanical issue). I keep mine on the truck all the time, rain or shine, staying in one spot for weeks or just popping off to the corner store, the camper stays on. It's not like the decision to hook up and drag a 40' trailer to go to the store. Your footprint is practically the same with or without the camper on, so it's an easier decision.
If you follow the truck camper forums and websites, a lot of people who spend large amounts of time in their truck campers keep the campers on the trucks permanently. I don't know if its the majority or not.