To augment Fred's comments, you should know that although blowing out lines may be adequate for other rigs, coaches with hydronics should have antifreeze added. Water that may not be completely removed can coalesce in a unit’s coil and still freeze, resulting in enormously expensive damage. The risk is generally held here to not be worth it.
I too, James, came here from a furnace and hot water heater, gasoline propelled format. I continued my blowout routine for awhile, but morphed to the security of antifreeze after reading enough experienced commentary. Prevention is a whole lot cheaper than the cure when it comes to AquaHots.
Also, if you have a clothes washer, add antifreeze to its tub and run a spin cycle. If you have a fridge with an ice maker, consider manually cycling it while under air pressure to get water out of the solenoid in back of the fridge. Further info about winterizing these two accessories can be found online, or we can further advise as needed.
Joel