Using blocks under automatic levelers

2x10-2x12 blocks will split even if doubled. 3/4 treated plywood cut to 10 or 12 in square can be glued together as thick as you want. I went to a truck dealer and got used heavy duty mud flaps and put on the bottom. Makes cleaning much easier also a small ice scraped takes of the heavy stuff. I use them under the jacks at all times even on black top you don't leave an indention. Most rallies won't let you use blocks that are painted.