I have the small one shown in the post of NM448 and have it rigged it up on top of an inverted milk crate so I can attach a long hose and run it all night off of a 20# propane bottle that sits outside my 19' trailer. When it starts getting real cold out I then use my Big Buddy hooked up to a 20# or 30# bottle. Very seldom do I have to run it at more than the middle of the three settings so that only one of the two burner pads is on. With both turned out at the high setting it will run you out of the trailer in less than 5 minutes. Very seldom do I even run my built in trailer furnace since the motor is noisy during the quiet nights out in Wyoming. It's handy to take the chill off if we come in during the day though and the portable ones can be kept out of the way and only used at night. I always have the roof vent open a few inches along with the window where the hose goes out to the tank and always use a good CO monitor as an extra precaution.