Hello licamp,
Probably not much help for you, but I drove Buffalo NY to Myrtle Beach last year. On a separate trip, I also did Buffalo to OBX. What we did was left late the night before, drove 5 hours and stopped overnight in Pittsburgh (One trip Flying J's and other Cracker Barrel). Both trips, we took the 81 and cut over, just to miss the DC beltway, which I hear is a nightmare and I won't drive it in an RV.
For the Myrtle beach trip, I think we planned another Flying J's overnight in Florance off the 95. However, we made good time and decided to drive directly to Myrtle Beach. Arrived at 11pm or so. There is a Cracker Barrel on N. Kings Dr that we stayed overnight. Had a nice breakfast and got to our destination bright and early in the morning.
Kris