With our 40' motorhome and Jeep we easily fit in Mammoth, Madison, Bridge Bay.
Here are some sites for the campgrounds and also for Fishing Bridge pictures Note that some of the campgrounds don't accept reservations so you'd need to spend the previous night closeby and get to those campgrounds early morning. It's doable. We didn't have reservations.
Also, be sure to plan on staying in Grand Teton Nat'l Park, also. It's altogether different from Yellowstone and is a beauty. Colter Bay RV is the place for hookups and Colter Bay campground (next door) and Gros Ventre are dry camping and no reservations but both have 300 sites. We've always gotten one.
Fishing Bridge PicsYellowstone Campgrounds