SCA reenactor who has done plenty of cold (although not like sub freezing) camping.
Most of us have lots of multilayered bedding, air mattress covered with blanket, then fitted sheet over that then several blankets. I personally have a futon pad and I LOVE it. Was just at an event this weekend, got to 56 at night…1 sheet and comforter…no problem.
Button up tent good, make sure you didnt leave a 4" gap somewhere or that you dont have little roof flaps that are open. and dont forget to pee in the empty gatorade bottles so the warmth can contribute, also saves you from opening up the tent if you have t go in the middle of the night.
I have seen one large tent with something like this
but it was a 20’x30’ communal canvas pavillion… so not something one typically has for individual use.
What kind of nighttime temps are you planning on camping in?
Are you going to be out in the open on a mountain cliff or in a tent??
I have done my share of camping in the Rocky’s during hunting season and have never had any issues with my face getting cold.
Ice Diving is a whole different thing where I have had to cut dives short because i couldn’t manage my regulator because of numbness.
I have slept in double (as in one inside the other) Duck down bags on the ground, and sure wouldn’t ever want to do that again.