This subject came up recently on a site used by a lot of Canadian crossbow hunters who deal with a lot of cold weather. Many use portable doghouse blinds with small propane heaters, specifically the Buddy, made by Mr. Heater or the Coleman Sport Trac. There is a larger Mr. Heater, but it makes noise because of the fan. A number of people said they'd had deer within 12 feet or less of the blind while the Buddy or Coleman heaters were on. The doghouse is very easy to set up and very light. I use one for photographing wildlife quite a bit. The other option is expedition down, which I used quite bit when I was younger for winter mountaineering. It is incredibly warm, but very, very expensive if you're getting the Everest quality stuff. Mine wasn't cheap and I had it custom made 30 plus years ago, but it has been worth every penny. For deer stand use, however, the enclosed blind and heater is the best solution. Just found the discussion. Here it is:
http://www.excaliburcrossbow.com/phpBB2/viewtopic.php?t=16003
