In scouts we winter camped in lean-tos made from sticks and spruce boughs. We would build a wall behind the fire to reflect heat into the lean-to. It works well

In scouts we winter camped in lean-tos made from sticks and spruce boughs. We would build a wall behind the fire to reflect heat into the lean-to. It works well enough in a survival situation. It's best to just have a sleeping bag rated for the conditions. Gathering wood and stoking up the fire every 45 minutes is too much of a hassle.