If you have dogs, there are monitors you can get that will page you if the temperature in the vehicle gets too high.
Since I live in Texas, A/C is a must, I'd do one of two things if I were buying a Sprinter. The first would be buying a Honda eu2000i Companion (where one can plug the 30A cord directly into) and an extended run tank for it, which would be secured to a hitch mounted cargo rack, then at the campsite, moved well away from the van, but still secured via a thick steel cable so the generator doesn't walk off. If more than 2000 watts is needed, one can just get two parallel cables and another 2000 watt Honda, but the A/C on most Sprinter vans will run on a 2000 watt generator.
Another option is an Extend a Stay kit and propane bottles, but a propane generator chugs the stuff, so a 20# bottle might not last more than a few hours, and larger sizes can get unwieldy.