I agree 100% with Cloaked. From Spruce Pine, go south to I-40 and stick with I-40 all the way to Knoxville. You need to avoid those high mountain two lane roads along the TN / NC state line, esp towing a boat. If it does snow, those high areas get alot more snow that the area along I-40.
Take some pics along the route with your boat, and post here. Its a scenic drive.