if you wanted a completely leisurely ride - route 11 would be it...but its gonna be SLOW, lots of small towns. RT 11 parallels i81 so you can hop on / off as you desire.
you could pickup 340 at winchester & run thru Front Royal & into Luray....once your in Luray you could cut over to i81 via 211.
211 on that side of Luray isn't bad, a little twisty but not bad (much easier than the other side which takes you toward sperryville - which i would NOT recommend in a coach).
alternatively you could continue down 340 to Elkton & cut over to i81 on rt. 33 or just keep on 340 down to Waynesboro & cut over one rt 250 to Stanton there.
the ride down 340 is very nice - mostly 2 lane til Luray and then it opens up some - and then transitions back down to 2 lane outside of Luray - BUT - traffic isn't too bad usually on 340.