I have found that milk crates, replicas are available, are great for stabilizing things. The fact that there height isn't greater than the base keeps them upright.If a crock would fit in one of them and the crate was on some non skid you would probably be good to go.
I've carried 2 1/2 gal and 5 gal propane bottles in them in the back of a pickup and never had one go over.