My two years living MB and traveling daily in six NE counties SC, three SW counties in NC, getting up to 60 miles inland, colder winter months will be usually 40-50 at peak of day, 30-40 at night, with occasional cooler days, and sometimes, but rarely, sport-coat warm days. It was ususually 10 degrees cooler 10-20 miles inland. I wouldn't mind winters there again, but then I'm also OK with Arkansas, eastern Oklahoma, East Texas and Gulf Coast state winters. A lot of people look for warmer, but all of these areas are snowbitd destinatons, particularly NE Arkansas.
I would expect Charleston, down inthe old city, to be slightly warmer than MB. We visited Charleston only on nice winter days, It will be cooler inland, and most of the places you might seasonally RV around Charleston are inland, up the river from the coast.
Coastal Virginia, out on the peninsula, might be about as warm as Charleston or MB, because the Gulf Stream gets pretty close there during winter.
None of it is as consistentl warm as South Florida, which can also have near-freezing days, a couple weeks at a time sporadically.