Hi TomD et all

I've camped in 3 season tents in the winter. They can be drafty and get snow blown through them, BUT using a bivy sack over your sleeping bag will keep spindrift off it and make it warmer. I've seen it snow INSIDE a megamid tent - as they had poor ventilation and frozen condensation on the roof would break off in the wind and fall on us.

Double or single wall doesn't make much difference if the tents are of similar quality. Better winter tents have more sophisticated venting options - my fav is zippered roof vents. Two people in a tent is warmer than one.

As far as tent shape:
in a deep heavy wet snow, in a teepee shaped tent, the weight builds on the outer edges of a pyramid until it can snap the center pole. In deep snow you would actually have to leave your tent and shovel the snow off the outer edge of the wall to keep it from being pushed down. I remeber the loud snap as my moss pyramid tent broke under 2 feet of fresh snow.

We were using the pyramid for a cook tent and in all fairness - no one was in it to keep the snow shook off, but it would only have delayed the collapse.

I was sleeping in my Bibler Eldorado right next to the pyramid. The bibler has two poles that cross over the top center of the tent, the sides are pretty steep - much steeper than the sides of a teepee tent. When I awoke to the sides of my bibler pressing in on me, I sat up (still inside my sleeping bag) and put my back against the wall and pressed the other wall out to where it outa be, then I turned around and pressed out the other wall and went back to sleep. In the morning my tent was completely buried and essentially was inside a snow cave.

*** keep your shovel INSIDE the tent !***

***Leave your sled, skis, snowshoes in such a manner as to faciltate locating them after a snowfall.***
Jim