Would it work?

You find a trench, clear it out, dump your firewood in it, light it, then when night time comes you just cut down a couple of young trees and slap them over the top and make your bed on top of that. Since the embers are sealed in it'll keep providing heat throughout the night.

Then when you wake up and need a quick fire you just push your spruce bough bed into the hole and light that up.