The ice maker is the least of your worries.
The Girard Tankless water heater has a freeze protection system where the burner will turn on occassionally when temps drop to 35 deg. However, there is some plumbing that is exposed to the outside (outdoor shower and outdoor kitchen) and the coach is not well insulated.
If you are going to be exposed to temps below freezing for extended periods, you will need to be opening up the cabinets under the sink to get warm air in there. You will want to use a couple of ceramic heaters to provide additional heat in the coach, otherwise you will burn through your proane quickly running the furnance.
The fresh water tank is under the bed with the electronics so being on the interior of the coach and enclosed with some residual heat from the electronics, you should not have to worry too much about plumbing freezing there.
Ultimately, you will want to run the water from all of the faucets occassonally to help keep things from freezing.