We use the 
Hoppy Levels to tell us how much we need to raise each corner to be level.
I carry several pieces of 2 x 8 boards of three different lengths so I can stack them. they are beveled on both ends to make it easier to drive up on them. Getting them under the dual rear wheels is sometimes a pain but that will allow us to raise any corner up to 4 1/2 inches. Usually if we are within one inch I am very happy and 2" is pretty good. To make the refrig happy it only has to be within about 6" but that feels too much for me.