I found this through the power of Google.
RV Guests at Grant Village Campground
RVs up to 40 feet in length can be accommodated in certain sites. The sites may be back-in or pull through. As sites may not be level, campers and recreational vehicle users should plan accordingly. There are no utility hook-ups at this campground, although an RV dump station is available. The dump station may not be available early and late season due to freezing temperatures.
http://www.yellowstonenationalparklodges.com/lodging/camping/grant-village-campground/