Is anyone familiar with a Bothy Bag or Shelter. As I understand it, they're multiperson, water proof nylon shelters for emergency bivouacs in winter conditions. They're apparently common in the UK, but not so much in the USA. They're lightweight, and 2 (or more in larger ones) can sit in them, using their body heat to warm the inside space. A salesperson at REI was telling me about them a couple of days ago, and they seemed like a good idea to carry on winter day trips for emergency bivouacs. He described being able to raise the ambient temp to about 20 degrees inside while outside it's -10F. Here's a UK outfitter link he gave me:
Anyone add any more info or experience about these?