Leg supports for truck camper storage

Thanks everyone, this was very helpful. Yes I was talking about unloading the camper so that the legs are resting on top of concrete blocks and nothing is under the center to support that. Our driveway isn't paved so a rolling table wouldn't work for us.
RickW - your info was excellent. The way you describe the legs "walking" is exactly what happened last spring and I just thought something was wrong w/the camper, it is far from being new. Now I know that it was just that the storage spot wasn't level and we've put it in a different place this year. Now I also know to raise it more slowly next year! Thanks again to everyone!