Webasto heaters - Still working perfectly at -55°c & after 120 days of inactivity! I will not post a link as it contains a lot of marketing guff but anybody interested can just google "the coldest journey"
Can't do much about consumption as power is needed to turn the fan, but quiet is easy, just fit a proper silencer and tune the exhaust length and dia instead of a random piece of old tube off ebay.