I wonder about this myself. I can put a level on 5 different surfaces in my RV and get 5 different "level" readings. The dash and table seem to jive with each other. The kitchen counter is way off of those readings, and if I put the level in the compartment where the fridge is installed I get something different yet. Don't get me started on the rear bedroom, which has a downward slope as it hangs behind the rear axle.
I just replaced my cooling unit and DO NOT want to have to do it again. I've been trying to get it close by putting a level inside the outside access panel where the fridge sits. It doesn't make the rest of the RV feel exactly level, but it's close enough for sleeping and walking around.