Low Temperature Caravanning

We were talking with some farming friends this week, reminiscing about the time we visited them here in Shropshire, when we lived in the South. We camped on their yard rather than put them to a lot f trouble and at night it fell to minus 10C outside. So cold that the wet brakes froze on, on our 4WD.

We had a Bessacarr twin axle at that time, with lovely warm air heating and it was so cosy that our farming friends moved in with us for the evening instead of staying in their draughty old farmhouse. 

Which begs a question. Honestly, what is the lowest temperature any of you have ever experienced when caravanning?