If you're able to plug in at the campsites to run air conditioning then I think you'd be OK with a traditional type Class B setup like the Travato. Of course you could always run the Onan generator (if allowed).
Mike Wendland has a Roadtrek with the largest battery bank available in a Class B I presume - 1600ah lithium IIRC. He recently had this to say:
one night air.JPG
He noted 2 or more days as being a long stay and finds a place to plug in if it is hot and they need air conditioning.
Yan Seiner (Roadtrek employee) summed it up like this:
Yan drive often if using air.JPG
Running an engine or an Onan generator is not always permitted because of campground quiet hours or no idling rules etc.