I know this is too late for your trip, but the Little River Campground in Townsend, Tennessee, is quite nice. We live near the GSMNP, and we took our first trip with the TM to that campground. They have full hookups and WiFi.
Cataloochee Campground - Great Smoky Mountains Is by far the most isolated and a true adventure to get there but worth it. Have a reservation for sure.