White Mountains of New Hampshire -- the Kanc, Franconia Notch, and 302 make a nice loop (aside from dealing with Conway/North Conway traffic).
x2 or 7 or whatever on Skyline Drive/Blue Ridge Parkway.
I very much enjoyed route 1 in California in a car, and would not mind doing it in some RVs, but at least parts of it would be no fun at all in a large RV and some sections have length restrictions (and rightly so).
Route 8 through the Adirondacks is a neat road, too, and I don't recall any especially low clearances, certainly nothing my Class C doesn't fit under easily enough.