Regarding winterizing the air brake/air system. If the temperatures are really, really cold, way below freezing. Trucks have a unit that feeds air line anti-freeze into the system.
Living in Canada, with temperatures getting down to -40 at times, I can tell you that the air dryer will not solve all the problems. A coach in storage at these temperatures, when the temperature 'warms up' to just freezing, when started, may exhibit symptoms of frozen air ride valves, frozen accelerator pedal valves, etc. This is due to condensation forming inside the air lines due to the changing temperatures that freezes in the lines.
Before storing my coach, I solve this by using the air chuck that's provided by the coach manufacturer to be able to push air into the air system. This is provided to be used by tow truck operators that have to pressurize the air system so they can tow the coach. I pour air brake antifreeze/lubricant into an air hose, then connect it to that air chuck, which pushes the antifreeze into the coach's air system. I do that several times.
This has solved my air system freezing problems. I am thinking of installing an air system antifreeze system like the trucks have.
2016 Creekside 23RKS
2012 Ram 2500 Laramie 4X4 Cummins 6.7L