If you just want to just get from Harrisburg to Nashville, I would go I-81 & I-40. It's a nice easy drive down the valley on 81 and just west of Knoxville, it's an easy pull up onto the Cumberland Plateau on 40 west. Depending upon your time, what activities you enjoy, and if you want to stop along the way, there is plenty to see and do in Sevier County, TN (Pigeon Forge, Gatlinburg, etc) and lot's of camping spots.
Larry, Beverly & Pat
Pups - Sweetie, Coco, Bodie
2013 Thor Tuscany, 45', Freightliner chassis, Cummins ISL10, towing a Buick Enclave