I got my bus local to me.... I am in Dallas Tx area, it is HOT here. As my bus was local it is equipped with 2 AC units for use while driving. I got that covered, the front unit (which is smaller) is 35K BTU, so I estimate my capacity at 70K BTU while the engine is running. I assure you it cools down the interior very quickly and keeps it cool. The driver's seat is in front of the AC vents and as such is a bit warm...working on ducting a bit of air down from the front unit. My biggest concern is my dogs need AC when I am not in the bus with them, at least they do from late March through early November. I plan on using my bus as a large dog crate while I attend markets and shows at which I will be a vendor. This means several unattended hours, so I need a bullet-proof plan for environmental control so I don't roast my dogs. I cannot even imagine trying to run a bus with no AC in Texas in the summer. I was raised in Miami, Fl and as a teen we didn't have AC in our cars. To be honest we never cared. Now at almost 40 there ain't no way in any universe I would even attempt to drive a car with no AC. Maybe the world is hotter, maybe I am just less tolerant but either way I can't take it.
I don't know how expensive or difficult they are to get, but the Trans/air units in my bus are worth every penny I paid for the bus!