I did nearly two week on and off last Jan/Feb, some of it in minus temps I used a PLCE bag on top of a reindeer skin and I was toasty. That was in quite a small hammock for me, a bit like a thai one. Very enjoyable though. The kids were out for a few nights as well, they were in a hennessy with quilts and on foam mats, they never had a problem with the cold even when it was -4
I love the cold, well as long as I can keep warn!