Step 1: Prepare a pit. This needs to be 1.5-2 feet deep. Make it 18 inches wide per person sleeping there. Length is going to be determined by the tallest person. Clear the surrounds of the pit of flammable material as best you can. Edge the pit with the soil you extracted from the pit.

Step 2: Fill the pit with rocks to a depth of 1 foot.

Step 3: Pile your firewood on the rocks, starting at the centre. Work outwards along the length before you start moving along the width.

Step 4: Fire. Use the fire for cooking, boiling water, usual.

Step 5: As the fire is dying, you want to flatten it out across the rocks. Spread it to the edge, keep it from going out of the pit.

Step 6: Brush the soil back across the rocks, keep it smooth and even. Notice how the soil has been dried out by the fire.

Step 7: Depending on how much you are "roughing it", spread your bedroll out, or pitch your tent, over the pit.

Step 8: Sleep. The heat in the rocks will slowly seep through the ground, keeping the soil warm and dry overnight.