To be honest, its a neat idea but I am not sure why would would do that, if you really want to sleep outside do it, even with temp below freezing its very very possible, I've slept a lot of times in the wicklow mountains when it was very cold, you put up a fire you need a VERY good sleeping bag and you will do do fine.
NOTHING can beat the feeling when you wake up in the morning in a forest with the birds singing - its a real good feeling (probably DNA inprint memory of some sort).