Bear Canyon is our usual
Sunrise it too close to I-90 (although Bear Canyon isn't far)
the KOA was "ratty" the last time we used it, but that was 15+ years ago.
The state park referred to is at Three Forks, some 30 miles from Bozeman, not what I could call close. There a NFS campground up the West Fork (Red Cliff?) with services that I would stay at before SP
The only "mobile home" park that took RVs (when I -lived- there) was a pit and catered to, well, even I as a poor college student wouldn't live there (but that was years and years ago)