Personally, I do not like stumbling around the tank on the floor. Other than that, I would have no problem with having the propane tank inside the TC. This is especially true with a propane detector.
I have had a couple of Wave3 heaters in TCs through the years. I have found what works for me is a side window open about a 1/2-inch, and a cabover window near my pillow open about 1/2-inch. Preferable windows on opposite sides of the TC. I usually leave the bathroom vent open about 1/4-inch also. Not only does this provide oxygen for the heater, it also provides good ventilation for breathing and helps reduce the condensation. Even without the heater on, the wife and I tend to get headaches with the TC closed up. I'm thinking due to a lack of oxygen.
Wayne