Might try the headwaters at Flagg Ranch. It is located between the Tetons and Yellowstone and can take your unit with water electric. https://www.gtlc.com/rv/headwaters-campground
It is a good base camp. If you have one day, you could see the highlights along with roughly another hundred thousand people. I'd do a loop and hit Old Faithful and Canyon and/or try to make the run to Cooke City particularly if you like animals as not much on geyser stuff that way. Canyon area is a must imho. You can also hit the West Thumb area from the South easy. IF you have the time, there are "side roads" in Yellowstone. Those are the most interesting, dirt roads fewer people. We like the "Lake" area. Try to end your day there and if you are at Flagg, it would be about an hour from there or so but if you do, you can sit on the porch with an adult beverage of your choice with you feet kicked up and it is beautiful. Decent food buffet style least expensive in the park.
