Check out BNO. I know someone (more than one someone) did that with their coach.
For mini splits, you need to look at the size of the "outside" unit. The "inside" unit tends to be small but the outside unit may be too large to fit under a skoolie.
I had looked at mini splits before when I had a nice huge basement to put the outside unit in (the Eagle).
We installed window ACs in the BlueBird. One above the front windshield and one above the rear emergency door. They both look the same from the outside. Since I painted the covers to match the body, it's hard to tell they are there and they cool just fine.