[C&P RV]

I-77 which runs by Cambridge OH will take you straight south to I-40 in NC. From there you can go east to Raleigh and take US 264 - then US 64 to Rocky Mount and straight out to Manteo. You can cut across a triangle from I-77 to I-40 using US 421 that brings you to I-40 west of Winston-Salem, NC and saves about 30 miles. It's a good road (4 lanes) the entire way. Parts of I-77 through West VA are curvy but not difficult.
To get back to Martinsville, I would retrace the route to Greensboro where you can get I-73 to US 220.
In case you are interested, there is a campground at the NC State Fairgrounds in Raleigh that is open year round -EXCEPT October when the fair is going. They don't currently take reservations - only space available, but we've never had an issue getting in except around the end of Sept. We were there in June for a week. Google NC State Fairgrounds camping for more info. The security officer told us they were looking at implementing reservations as soon as this fall.

Happy trails!