Hugh, this is from a very old post. Spenser back then told me 1 or 2 tea type candles provided enough heat output throughout the night for him, and his wife, to sleep comfortably. They could start with more candles and blow some out once it warmed up enough inside. Years have passed since our conversation so I remember/know few more details. The four tins in his setup had (my best guess) 2 to 4 sq. ft. of surface area to radiate heat. They were a mini version of a gas wall heater in a house.
If each tin was 8" x 8" x 3" there would be nearly 1 sq. ft. of surface area per tin - counting the 8x8 top and four 3x8 sides. So for a small cabin area there could be a substantial surface area of heat radiation.
His one side door was not air tight and there were two awning windows for ventilation. i have no idea how much insulation there was in his trailer.