I don't have A/C on my skoolie. With the hot tub, trying to make cold air is counter productive.
Instead, i use fans in the summer. I can't believe how wimpy most electric fans are (12 or 120 volt). In my skoolie, i use electric radiator cooling fans from small cars. They're super cheap at the junk yard. 10 - 20 bucks. They're very reliable, not too noisy, and move an unbeliavable amount of air.
My skoolie is painted black. Black paint and the hot summer sun makes for a less than desirable combination. Even when the temp is 90 (that's about the hottest it gets here in MI) life in my skoolie isn't that bad with the 12v colling fans running.
I'm not sure how much energy they utilize, but i can leave one fan running for several hours using my very limited battery bank. If a rheostat were installed to control fan speed, energy consumption would be much less.
My skoolie engine is running most of the time i'm using the bus, so energy consumption isn't a big deal for me.
Quis custodiet ipsos custodes (who will watch the watchmen?)