G’day JR,
I was waiting for the smartphone inclinometer suggestion

I’m certain they have been mentioned here before as levelling devices.
Apart from my dislike of these big, heavy, battery gobbling things I wonder about their accuracy. They decide which way is up using a 3 axis accelerometer chip that I have explained here several times as used in brake controllers. If the van track was say 80 inches then each inch in height difference would be an angle of 0.72 degrees. That is a fairly small angle and a smartphone error of only 1 degree would make it useless.
The other issue I have with using a phone as a level is their length. Unless they are used on dead flat surfaces they can produce wrong results. A level needs to span the peaks and troughs to get a true average value. I know on my van floor that I get different angles in different places as it drops between the chassis cross-members.
The best place to check whether the fridge is level is along the bottom of the fridge. Lateral angle is not very important for the fridge.
Whatever it is that you want level in your van I suggest once you have it perfectly set up then choose a single spot, preferably at a comfortable height on a bench, where the spirit level shows true. Always use that reference spot for future checks, as I will with my calibrated wedge
