To be honest, you should not be using your coach as a campsite compressor -- starting your coach and not driving it is something nearly all engine and chassis manufacturers recommend against. When started, it needs to reach operating temperature, which can ONLY be achieved by driving it. Otherwise, you are just leaving excess moisture in the engine - not good! It is not like a gasoline engine that you can exercise at idle... water temp is not what you need to be concerned with on a Diesel - it is oil temp and again, that can only brought to operating temp under load.
Sorry, not trying to lecture... but really - you should have a proper compressor.