I stand to be corrected, but muy understanding is 102 inches is the legal width. Until several years ago it was 96 inches, but perhaps there are some local road restrictions, though I have never come across any.
There are weight restrictions in effect on some roads and bridges, and height restrictions for some underpasses. These can be learned by buying a trucker's atlas at any truck stop.
What year/model of motorhome were you looking at?