My impression from videos and comments is that driving up the Montana side is easier than the Idaho.  It's not as steep, and relatively open, basically a ranch road that climbs.  Still only you can judge whats safe for your RV.
I haven't driven it.  Last time through the area I camped near Salmon (BLM) and crossed over Lost Trail Pass.  This was early June, and we actually got snow flurries at the top.  I checked out the road to the east that goes past a battlefield memorial site, but decided I didn't have time to go all the way.