I have bought a couple of batches of Diesel night heaters (still have a couple from the last batch
) which have been well received, and they do make the difference between being very uncomfortable in the cold, and being very comfortable 
At this camp (Easter 2013 in North Yorks), we were kept warm in -9.5C temperatures by 3 firepits, alcohol, and some of us had night heaters
Steve and I braved the snow on another camp in March 2013:
Though Steve found his leisure battery was failing and so the heater wouldn't fire, and his gas froze!
I was fine in mine though, night heater and gas on for the kettle for the hot water bottle
Hopefully Julie will be able to join us on one or two camps, possibly not as cold as those though.
Cheers,
Robin.