I used to do the nylon tent with no heat thing. While it is possible, it is not comfortable. I froze my ass off and drifted in and out of a very light sleep all night. One trick is to boil a bunch of water and pour it into your nalgene bottles, then shove those bottles into your sleeping bag. It will keep you warm for a few hours, at least. Also bring a bunch of wool army blankets to put under and over your sleeping bag
I've since learned that the only way to do elk camp is with a canvas outfitter tent and a wood burning stove. It keeps the whole tent warm and toasty, and when the fire goes out--its time to get up and hunt.