jim---myrtle beach will definitely be warmer than hatteras, but not hot. we've been there for feb and march for the past number of years and often it's quite cool.
we quite like myrtle beach state park but huntington beach is also nice. there's lots of private campgrounds as well and all will have room. in fact, driving down the main drag will be a little disconcerting at first, seeing motel/hotel rooms advertised for less than what you'll be paying at the state parks!
check out the "deal" offered by the state park for longer stays. generally a good deal.
and if you do decide to go and are a campfire afficionado, i can PM you with a # of a guy to buy a bulk load of firewood from---if you're there for longer than a night, it's a much better price.