Air conditioned storage unit big enough to park in for a few months?
Idle the bus and have a big inverter (2 or 3 thousand watts i'd imagine) to power a nice sized air conditioner AND a remote monitoring system in case bus dies/etc
hate to state the obvious, I realize your work is not mobile, but drive north?
dude tell your boss your gonna quit if you can't bring your dog in during the summer, I mean I get if it's a health code thing (like working in a restaurant for example) but there's no reason he cant chill in your office or whatever with you assuming he's well behaved. it's well documented to improve overall employee moral - not just for you either for everyone there
Also, in regards to the very real potential for mechanical failure while your gone (thereby making the AC turn off) you can install a backup generator to fire up when it reads your battery bank voltage going below a certain threshold. I've never done it, but I know its a thing.
oh yeah, get a generator too, just plug the AC into that. make sure its a gen that can continuously operate, many of the cheaper ones have limited run times.