hd, First, when you created your profile, you said "Yellowstone" for location. That's so folks on here can see where you're starting from when giving directions. City and State is enough.
Second, YNP was created 36 years before the Model T was invented. So campgrounds came along later. As a rule, the site measurements are the maximum size it can hold before you back into a tree. Some CGs have larger sites, but Fishing Bridge is the only one with hookups - inside the park. I'd consider Grizzly RV park in West Yellowstone, MT. Long pull thru sites with water, electric,sewer and cable TV. And only two blocks from the West entrance gate to YNP.
Retired and visiting as much of this beautiful country as I can.