Hi Lisa here in Mount Pleasant, SC (near Charleston). Stumbled on this thread when i started planting sweet potatoes last year and had a great harvest, and am now hoping to salvage whatever is left in the ground over the winter.
I have been putting pinestraw, mulch (cotton burr, compost, etc) on top of where the plants/vines were and also some plastic on extremely cold nights.
just today i found 3 potatoes fairly close to the surface that i missed, and they look pretty good. I went ahead and dug them up and they are outside "sunning" as i type this. I will bring them in this evening where they will remain until i eat them

It is supposed to go back down to like 28 tomorrow night, so i will put the plastic back down out there, but i was so pleasantly surprised to find these babies today (and still looking good).
Maybe one "burnt" (with cold) little spot on one. I don't know what they will look like or taste like when i eat them, but i'm a happy camper and am trying my best to "over-winter" them.
just wanted to say hello and will hopefully have a good report when the cold weather is all over with around here!!
Cheers,
Lisa