I hunt elk/deer during the archery season in colorado each year with my dad. We pack horses in and use a wall tent. My dad is getting up these in age and is cold reguardless of bag used. We have been looking for a propane type heater (buddy heaters) and I've read that they don't work above around 9k ft. Our tent is at around 10k ft. We don't want to go with a wood stove because of the hassel of keeping wood stocked. any suggestions?????