We have stayed both at Fishing Bridge and at Grizzly RV in West Yellowstone; both CGs have FHUs. Grizzly is more pleasant to stay at, IMO, but it does require a 28-mile roundtrip drive just to get to the Grand Loop Rd. - on the other hand, there is almost always wildlife to see in that distance, and some nice picnic areas, scenery, etc. Fishing Bridge is well-located, pretty central within the park, but the atmosphere is crowded at best, and with a long rig & long TV, you may find backing into a site there to be quite a challenge. (We had enough trouble with a 27' TT & standard size crew cab truck.)
You should be able to make reservations at Fishing Bridge for next year already; at least for the hotels in the park, reservations open on May 1 for the following year (i.e. May 2015 for the 2016 season).
If you're staying 5-7 days in the area, you might consider staying at 2 different CGs. There is enough variety in the park that you'd get a different "feel" from 2 separate CGs. Of course, you would spend some of one day just moving from one CG to another.
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2020 Toyota Tundra CrewMax 5.7L V8 w/ tow pkg, Equal-i-zer
2020 Lance 2375