I'll second the no heater... I hammock tent, and I've gone down to about 20 degrees. The underquilt, fleece liner, and top quilt have been all the heat I need. I love winter camping, because there's less people out, no need for bug nets, and campfires feel good (last trip I was on it was 80 degrees and someone lit a fire. Seriously? I don't want to sweat more!)
I do take chemical hand warmers for emergency use, but I haven't used one yet.