If you can manage off grid, then there are other campgrounds in the park other than Fishing Bridge. Note that the nite time temperatures in Yellowstone even in the summer often dip into the 30's so there is little need for air conditioning, the campgrounds do allow generators during the day, so it is possible to recharge your batteries. When we were there last summer we stayed at Grand, Canyon and Fishing Bridge campgrounds. Grant and Canyon both had dump stations, Fishing Bridge is the only full hookup campground in the park, it is also the one with the tightest spacing (sardine can like), and as mentioned will be close for renovation next year. The others are very large, and spread out, though the spaces and camping loops can be tight for larger RV's we had 30 ft spaces at each with a 28 ft class A (29'5" bumper to bumper) and barely fit in all of our spaces, so when they say 30 ft they mean 30 ft not 31 or 32. These are older campgrounds and were not designed with todays wider RV's in mind, the camping loops have curves, with narrow roads and nearby trees, on one of the camping loops while going around a curve I know I had less than 12 inches of clearance on each side between a tree and the corner of an RV in its space. Hanging off the back of the RV sites was not an option at any of our sites either, as all had saplings growing up at the rear edge of the pavement.
2002 Safari Trek 2830 on P32 Chassis with 8.1L