I picked up one of these portable gas heaters yesterday to use on an upcoming camping/ observing session.
www.bcf.com.au/online-store/products/Com...menuFrom=20305#Cross
At this time of year the regular dark sky site can drop as low as minus 10C but will probably be close to freezing. These units or ones similar to them are available in Ireland/UK in camping stores. It runs on a disposable 220g gas cartridge-the ones used in the Asian portable stoves which are cheap and easily available.
It puts out about 1.5KW and will run for 2 hours on max output. Its great for taking the chill out of a remote observing session and should make the difference between packing it in due to cold or staying that extra hour or two. Its quite small and light too.
Highly recommended for those cold Winter nights-especially for imagers.
  