I camp in jeeps, often at about 9,000 feet above sea level; but now I rarely go camping in the winter (getting too old).. therefore, the following does not apply to tourists...
However, in my experience, warmth is better several layers of clothes and a warm sleeping bag (my multilayer, than my clothes; outdoor warm bag, inner lining for a poncho (military uniforms) and, finally, the inner lining for the handbag (cheap plush bag for the night (wallymart)) IF it gets really cold, I can wrap a military rubber bag powered by rain poncho, but this means that the next day I will have to dry the bag and its diapers... I only sleep in boxers and a beanie.
I use a crib with foam padding (cut the 3-inch foam padding (including fingers) for the hospital bed) sometimes I also use the Coleman padding that is attached to the crib.
I tend to have cold feet and I've tried a lot of products, the best one right now is a fluffy bath mat (walmart) that I can get and slide off the floor to cover my feet in the middle of the night.
I've tried a lot of heaters, but at best they only work well to heat the tent before you get in or out of the sleeping bag... be careful to always leave suitable vents within ten when using an oxygen consuming device, I don't sleep with the tent heater on.
Every few years here, someone will kill themselves trying to heat a camper, tent or paddock with charcoal; learn how to shape their disappearance.
Beware of hypothermia; several people have already moved to the camp, showing symptoms in the winter. After warming them up, I took them back to the city; if they hadn't found us, they might have been found in the spring... or not.
