Did a few cold January night's during basic training and would do it again if I had the gear. The sleeping bag is the key and as mentioned above keeping it off the ground is key. Our cold weather sacks looked like mummy bags and we kept the boots inside the bag which is not that comfortable but not having cold boots is a big benefit. For the ground I would do a ton of pine boughs and have a roll up pad on top, forgot what we called them. I saw something this past winter where a group of guys do this as a annual this and it has been growing in size ever year, pretty sure it is in WI