I've been using it a couple of years in the annex with no problem. The Little Buddy Heater is specifically made to use in tents. It will shutoff if the o2 is to low or if it falls over. If the weather is ok I'll sometimes crack the skylight or a window, but if it's raining we leave it sealed up.Awesome trip. Quick question for you tho about the heater buddy. I have the Mr.Heater buddy and am always scared to sleep with it on in the annex, did you guys have any issues? Did you leave windows cracked or anything? I now have a carbon monoxide detector I bought just to be extra safe.