When I'm working on my tractors, or other heavy stuff that sits high off the ground, I have an assortment of big wood blocks I acquired from a local sawmill. Some of them are over a foot square, and a couple of feet long. They're leftovers from when a squared-off log is cut to a standard length before being sawed into dimensional lumber. A stack of those things, overlapped properly, can support several tons of weight, even on a less than ideal surface like dirt or gravel. Just be sure the base layer is level by digging or filling in low spots before stacking up the blocks. The bigger the footprint, the less weight each part of a stack of cribbing has to support.
Jerry
