Some time back, another site - Zombie Squad - would sponsor a Mock Bugout Contest. Great fun and they had some cool prizes. One winter I entered with a cardboard box shelter. a simple triangle shaped cardboard shelter. . The door was made from the same source box - a fridge box obtained from the local Home Deport for the asking. Duct tape was ordinary - the 3 inch Gorilla tape would have been an expensive upgrade. I made the door so it would almost seal. Friction fit, it had a small gap at the bottom.. The orange container was to avoid late-nite trips outside. I used a 5.5 lb blanket over and a USGI pad under, with a Refectix underpad. Under the shelter was another 3 layers of cardboard. Was comfortable at well below 0F. Me under the blanket. My Alaska rated parka made a nice pillow. Thee was barely room to turn over. Small space = less air to heat. I was dressed in a polypro base layer, a set of felt booties and a wool beenie. I had a UCO candle lantern, but since these only produce (at best) ~80 BTU, it would have taken off the chill, but it isn;t something that will keep you warm - that is the job of the insulation. I my 12 part DIY survival kit (A DIY disaster kit. A twelve part series to make your own kit.) I had mentioned living in a cardboard box - this is the box. Suitable only for a couple of days, it did keep me warm enough to sleep comfortably,. A real shelter was discussed (Building your own evacuee shed/house/home) in another thread.