We've camped at Uwharrie (agree with Gordon2's analysis) and Morrow Mountain (NC State Park gates are locked at night; hours probably from 8 PM to 7 AM in October) and enjoyed our stays at both but I'd suggest a different route.
From Charlotte, take I-85N to Greensboro where you can overnight in Hagan Stone Park Guilford County Government | Camping
(4hrs 50 minutes per Mapquest). From there, take I-40E to Raleigh and then US-64E to Nags Head and then NC-12S to Rodanthe (4hrs 49 minutes per Mapquest).
Hagan-Stone is ten minutes from the interstate. The rv sites are close together and located in an open field but there likely won't be more than a half dozen other campers so space and privacy won't be an issue. Price for water & electric hookups is $20; $18 for seniors.
When leaving the rally
, consider taking the ferry from Ocracoke to Cedar Island and then US 70 back to Raleigh.