This is a real simple question to answer. The drive from the RV parks in West Yellowstone as said is about 17 miles one way to the junction with the south loop road. It is another 10 miles to the Norris junction that is the meeting between the north and south loops.
Yes, Fishing Bridge is a tight park and it is not cheap. It is the only FHU in Yellowstone. In our case, it was not worth the fuel and time to stay outside the park. Your Mileage May Vary.
If we had a towed, it might have been worth booking in West Yellowstone. One thing to be sure of is that it is worth the effort and expense.
Matt