Here are some photos of Fishing Bridge. I've seen worse RV parks and they are truly parking lots. This at least has trees. The sites are such that you park your RV to one side of it and your vehicle on the other side.
If you want hookups and are there to see the park, this is the place for you. Typically folks pack their cooler, leave early in the morning to tour one section of the park and return toward evening - very tired and ready for bed. Then they do the routine the next day to another section of the park.
So for convenience this is the place to stay.
https://www.yellowstonenationalparklodges.com/lodgings/campground/fishing-bridge-rv-park/
