Campground on I 81 Virginia

There isn't much right off of I81 near Roanoke. You could try the Natural Bridge/Lexington KOA about 35 miles north of the I581 junction at Roanoke or Dixie Caverns a little south of Roanoke. Dixie isn't great, but ok for an overnight. The KOA is pretty busy this time of year, but you might catch a break depending on your rig size.