I am against putting the gas bottle inside. They tell you these things for a reason, and that is the leak potential. I would not worry about propane in cold weather. Propane starts to boil at -47 F. Butane, on the other hand, starts to boil off at 31 F. So as long as it is over -40 F, I would not worry about having the bottle outside. Millions of homes are heated in the Northern United States with propane tanks sitting outside.
My cat heater which is mounted on the credenza, next to the fridge, is tapped into the fridges line, with a "T". Most AS have the propane plumbing mounted on the underbelly skin, so it should not be a problem to tap into it for an aux heater.
2003 GMC 2500HD 4X4 D/A Ext. Cab
Propane Powered Honda EU2000i
Lots of Hot Sauce!
Air # 283