March is a bit of a gamble on the OBX. There is a lot of pleasant weather then, although of course too early for swimming, but also some late cold snaps come through. The t/s resorts generally end up mostly full that month, but the demand is off enough that you can find inventory a lot closer to use time than higher demand periods. I suspect you would not have any trouble right now finding availibility for next March.
The best coastal choice in NC would be North Pier Ocean Villas in Carolina Beach, close to WIlmington. The weather will be a bit warmer, and you are close to Wilmington, a fair sized city with some interesting things to do.
If you like skiing and snow, the mountains may well not have natural snow on the ground in December, but the ski slopes will likely have machine made snow.