I've run a Buddy heater in my pop-up ice shelter. After a few hours, it's raining inside, but we also keep the shelter buttoned up to hold in as much heat as possible when it's 20 deg. or below outside.
There is also some information on the net about using unvented heaters in enclosed spaces and the pollutants, besides CO, that people are exposed to in the inside air.
I'm not saying it can't be done, just don't think it's smart to do it overnight when people are sleeping. I had one in a hard sided ice shack. Had a friend who is a heating and air conditioning specialist looked at it for me. He asked me if I would trust my life to a 25 cent oxygen sensor that was likely made in Mexico? That week I bought a heater that exhausted through the wall and drew intake air from the outside to replace the Buddy.
Many years ago, I mounted a 3 burner propane cooktop in my ice shack that I salvaged out of an old pop-up camper. I was sitting in the shack by myself one night when I began to feel woozy, real woozy. I kicked open the door and felt a rush of fresh air come in and my wits came back with it. I then began to look real carefully at the cook top. After popping off the top, I discovered there was a pilot tube inside that I never knew was there. It was glowing with a real yellow, dirty flame. I blew out the pilot, and after that, never used the cook top again without turning off the propane afterwards. I figure I was 10 minutes or less from losing consciousness, and buying the farm. A lot of people have died in cabins over the years from the pilot lights on Servel refrigerators. Be very careful with unvented flames of any type indoors! CO poisoning is almost impossible to come back from without some adverse consequences.
