Inside, keep your body off the ice or ground (the Inuit put their sleeping blankets on top of a bed of sticks and reeds) and create heat-trapping "loft" (it's what keeps you warm in a sleeping bag) by layering a few small blankets or big trash bags, with leaves or crumpled newspapers in between.
Firefighters turned on a portable heater to keep her warm in near-freezing temperatures while they dropped an air bag into the opening to slightly spread the walls.