Consider this route:
1. Gaffney South on I85 to I26.
2. I26 West to:
2a. I40 if Westbound is open from the rock slide. Go to NCDOT: I-40 Rock Slide News & Information
for current information
2a1. I40 West, exit 440 to Route 321.
2a2. Route 321 to Gatlinburg.
2a3. Or continue on I40 to exit 431 (I think) to route 411.
2a4. Route 411 to Sevierville.
I've done 321 and 411 with a coach and toad. While there are a couple of turns that can wake you up, overall the roads are okay for a coach and toad.
2b. Continue on I26 West To I81
2b1. I81 South to I40 West.
2b2. I40 West to exit 407. Follow the signs to Sevierville.
For me, I'd still to the Cherokee route through SMNP as a first choice. I've done it several time in the coach/toad. For me it is no problem.