I have used scrap 2 by 8 treated lumber with a 45 degree cut on one end. About 2 feet long. Used for years. Effective and cheap. And remember, you cannot run a RV refrigerator when it is not level. Makes it quit working and expensive to repair. Hope this helps.
1993 Gulfstream Sun Voyager DP 30'
200 HP Cummins B5.9, 4sp Allison AT542
Toad 1998 Honda CRV, 2006 Honda CRV
Life's too short to drink cheap beer