Mowdoc... To me, there is never enough air conditioning. Two units would be the bare minimum in almost any medium sized unit. I always thought if I ever bought a class B, I would still have two units, if one went on the fritz.... you will still have air.
I know this is apples and oranges.. but, we have four 13.5K units. Even with three units running it will freeze you out. The manufacturer uses a computer program to design the venting so that there are no 'hard' bends to restrict air flow. That's why we could go with 13.5 units vs. 15K units. Also, the 13.5 roof design is lower.
The amount of air flow that we get from just one unit is amazing.
Go with at least two units on whatever you buy and nothing less than 50 amp. service.
Safe travels,
MM.