We use the Big Buddy every time we camp and never had a problem. First time brought a CO2 detecter just to be safe but it never went off. We have been down to 18 degrees F and been in shirt sleeves in the tent.
You might want to check out this tent. http://www.amazon.com/gp/product/B006FMAO08It's called the Standing Room 100 hanging tent. It attaches to a 10'x10' canopy/gazebo. Here is the product description: The Fast Up "Standing Room" tent is an excellent shelter with vertical walls that most people...