Good point Joe. In the garage the big door quickly get moisture on it to the point of running on the floor. The same on my trailer except I have power vents so it is not as bad.
I have this same heater. We used it to heat the 22 x 24 garage. It takes a while to get everything warmed up when it is in the 0 or colder but it works great. The CO can get a little high before it cuts off. I'm very sensitive to this and I can feel the effect in rosey cheeks and head ache way before the heater kicks off. I have a fan on mine and it works quite well too.
I use it to warm my trailer too. It doesn't take long to get nice and toasty in the winter and there is good ventilation in the trailer so CO doesn't seem to be a problem. I also have a CO detector in the trailer.