Since the refrigerator is the most important item to get level, I placed our stick-on levels on the front and side of the fridge.
For our wheelbase, we can be as much as 7 inches out of level front to back or side to side and still be within the allowable range for the fridge. For our personal comfort as well as having a safety factor for the fridge, we keep out of level to be less than 3 inches either way.
We find we very seldom need to use our lego blocks in an RV park. State and federal park sites are more apt to be out of level.