Carbon monoxide is a byproduct of incomplete combustion. So as long as you have enough oxygen for the propane heater it will be ok to use indoors. While Carbon monoxide is odorless, the symptoms can't be ignored. See
http://en.wikipedia.org/wiki/Carbon_monoxide
According to the Mr Heater website, their heater is equipped with the oxygen depletion shut-off valve.
http://www.mrheater.com/whatsnew.asp?id=146
Unfortunately it is so sensitive that you can't use it in the high altitude locations above 7000 ft where it really gets cold.
The Trailmanor does come with a Carbon Monoxide sensor for added safety. Also the Trailmanor is not a sealed unit. If you want to be safe, keep a couple of windows open a little.
But what about the propane stove and oven? But since I don't believe it has a oxygen depletion sensor you need to be concerned about ventilation.
Safe Camping,
Bob Wilson