You can make a solar heater from soda cans. Google it - its on You tube. It produces temps of up to 150 degrees ???
But you need the sun to be out -so for night Down comforters, woolen hats, put up blanket or divider to make a small area around the bed to keep heat in. And sleep with others for body heat. You'd be surprised how much heat people make. There are also Gas space heaters, just make sure you have a Carbon monoxide alarm.