Much better than the snow and sub-zero in Montreal.
PB: -41F windchill in Montreal now :B T'will get MUCH colder tomorrow!
Camping in ANY locale above 0 F would feel balmy in comparison!
The only down-side to camping directly on the SC coast (for me; YMMV), would be: more persistent rains in December/January (ie. long periods of rain without sun because this region is the transition zone between arctic fronts and warm humid air from the deep south during winter) and high humidity = uncomfortable without persistent heating going on in camper.
I find personally that high humidity when temperatures are from ~~25F to ~~55F make camping very uncomfortable (humidity leaks into camper like a sieve). I would prefer camping in either temperatures between 20F and 24F and dry (humidity below 50% RH), or regions where snowbirding temperatures are always above 56F (to the mid 60sF up to low 70sF on occasion) with humidity anywhere from 50s% to ~80% RH (Savannah, GA south to St Augustine, FL in winter).
I suppose that snowbirding from Myrtle Beach to St Augustine would offer the advantage of being a far less crowded winter destination?