Leg supports for truck camper storage

We had our Sunlite truck camper legs sitting on top of concrete blocks for winter storage last year. Last spring while installing the camper back on our truck the rear legs shifted and the rear part of camper ended up falling off both blocks and ended up in a very precarious place. We need to use something as a base as the truck is too tall to just set the camper legs directly on the ground, what do others use for this? I'd like to avoid having the camper fall again next spring!