Teardrop Furnace Install

I have a popup apache camper with a furnace which I have found useful in the mountains. I am thinking about putting one in my teardrop project. I have seen a few pictures of teardrops with furnaces. Does anyone have pictures of how they installed the furnace in the camper? Are there issues with carbon monoxide and fresh air? How many BTUs would I need? I see there are some used ones on ebay such as atwood. Any suggestions?
Thanks,
Thanks,