i talked to a fellow at a canoe group meeting who had done some winter treks thru canoe country in winter at sub zero temps.he said they just found a sheltered place to camp and kicked up a wind break and slept under tarps without making fires.meals were simple and cooked on camp stoves.the sleeping pads and new bags were all they needed to stay warm.he said if you made a fire you hung around it too long so they had quick breakfasts and moved out on skis and that kept them warm.a friend who i did some hut camping with in cold weather had also winter camped with just a tarp set up as a lean to.he also felt that the modern sleeping bags along with poly fluff pants,soxs and shirt were enough to stay warm at sub zero.he also liked the idea of being out in the open,the only "bad" part he said was the early darkness as you can only hold up in a sleeping bag reading for so long.
for survival i would make a snow cave where the temps inside can be well above freezing..think igloo-however--with sleeping bags only rated for summer/fall temps and without true winter clothes i would want whatever i could get into a tent to warm it up.most tents have a vent so you could run a stove or lamp and tents were made with cook holes in the floor for a stove...this is running on--so as a last bit at 1:20 AM i'll say that i have done the hot rock trick.on a very cold fall canoe trip with sleet and rain i heated several bread loaf size rocks very hot and put them on top of a few small rocks to get them off the ground inside the vestibule of my tent with it closed up and the door open and that warmed the inside enough to get comfortable and pull things together before getting into the bag fully dressed in fresh dry clothes..i have to stop doing these posts so late at nite--more and more thoughts run past me----