I have done a fair bit of winter camping over the years. early on just in a sleeping bag on a frozen lake, then in a tent, in a small homemade trailer and in a small insulated trailer I built last summer. For tent winter camping a good sleeping bag is the most obvious piece of equipment to have. The next very important piece is a closed cell foam pad to insulate you from the ground which acts as a heat sink, so insulating yourself is very important. Never put your head inside the bag, the moisture from your breath will take away the bags insulating qualities. Use a mummy bag with the hood down over your forehead so just your eyes, an nose are outside. Or wear a toque and if you can stand it lay a sweater over your face to keep the cold off. A candle lantern in a small 3 or 4 season tent works pretty good, but remember it too gives off carbon monoxide. Like an earlier post said, a small tent is easier to keep warm in than a large one and a vestibule is the place to cook. One idea I,ve been thinking about for a tent on a trailer would be to have a propane catalytic heater in the trailer under the tent. I thought that if the board the tent sat on had some small holes cut in it over top of the heater some of the heat would rise and go through the nylon of the tent floor providing some warmth. The trailer would of course have vents in it to allow the carbon monoxide to vent out. I'm not totally sure it would work but I am looking for a bit more comfort and don't wish to give up winter camping, it is very nice and peaceful, no bugs, and no crowds.