I've seen the outdoor side of a mini split installed in the engine compartment of a bus before. Maybe you have room for that option.
A/C's are on sale. Buy two 12,000btu window units. Cut both in half carefully leaving the fan motor one one to power the inside unit. And cut the second leaving the fan motor for the outside unit. Even though you're buying two, still cheaper then a mini-split. Good Luck, TomC
I hung my mini-split on the back of the bus and it looks fine and works great without giving up any bay space.