Well, the lean to tarp with a fire in front isn't a bad way to go, I do pretty much the same thing, but if take it a few steps further and make a "Super Shelter", where you put a plastic front panel on the lean-to you'll be warmer and protect your bag from sparks and embers.

Here's a video that shows one way to set one up. I use a piece of single layer bubble foil insulation for a floor in mine, and i made a small "Baker's Oven" style tent out of SOL emergency blankets instead of using a simple tarp. Any condensation inside the shelter will dry up fast if you restart your fire in the morning.

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