The smaller the better.
We went up there last fall with our rig. The CG was full but we got to 'tour' it. It was a bit tight on the turns/hills trying to keep the roof from grabbing branches, the sewer drain from grabbing ground, the trailer from climbing something it shouldn't, and making the truck climb something it didn't want to. On top of that, it looked like at least half of the spots were nowhere near level. There were some larger trailers in there than mine.
I went to college at USU, and frequented Tony Grove a lot (but never the CG), but I will never try to stay in that CG again.
On that trip since the Tony Grove CG was full, we stayed at the Lewis Turner CG at the start of the Tony Grove Rd. Another 50% of spaces are near level. Better off just boondocking on one of the dirt roads off Hwy 89 for free.
The Tony Grove CG has potential I guess, maybe if I didn't have such a sour taste in my mouth from that trip I would feel better about it.
A 25' would manage just fine up there. A 30+ might require you to make a 3pt turn a couple times.
