Just a tip that works pretty nice on those cold nights when you just can't get warm. Just before you turn off the gas stove for the night, boil up a few pots of water and pour them into your nalogen bottles. Close up the bottles tight (leaking would really suck) and put them into the bottom of you bag (box). When you jump in your bag it will be like a heating blanket. Your bag will stay warm for hours. I have a LL Beans 0 bag for most trips above 10 degrees, below that I have a Northface -40 bag for the really cold ones. I get really cold easy, everyone is a little different. You'll probably have to try a couple of bags before you find what your looking for!