I don't think you want to wrap in plastic, on hot days it can overheat the trunk and help bring the plant out of dormancy too early. I don't have any strong advice since I never protected mine. I thought I would lose a few last winter but all were OK. You could try wilt-pruf or reflective bubble wrap insulation (the aluminum foil reflects the sun so no overheating problems).

Scott

The coldest here was 14 degrees a few years ago and the muscadines had zero damage with that temp. However, on the less hardy plants, encircling them with a 3 ft tall wire mesh fence cylinder and filling them completely with dry leaves helped a lot. Two foot diameter was my minimum,and the plants were in the center, but I much prefer at least a 3 ft diameter fence cylinder and taller than 3 ft where appropriate. Even when there was a heavy rain the leaves inside did not get waterlogged. The leaves stayed in place until Spring and then were released from their confinement to become a mulch ring around the plants. Inexpensive wire fence with the 2" X 4" spacing holds stacked leaves in place well.

Thanks for the thoughts.