I lose about a gallon a year of Aquahot coolant. There is no apparent leaks visible, is that considered excessive? we use the coach 4-6 months out of the year 10-12k miles. We do use the heater even in the summer tend to go north to beat the Texas summer heat.
Any cracks in the overflow hose (the one from the radiator cap to the overflow jug), especially at the ends?
It gets brittle with age and thermal cycling.
Have you taken the cover(s) off to inspect the pan and see if there is any coolant in the pan? Do you ever see drips from the overflow tube that exits out the bottom of the basement?
The system should not be leaking at all. Need to check all the hoses and heater cores especially in the front dash. Check that the pressure cap is working. You can do a pressure test just as you would for the engine cooling system. If no external leaks, then y need to look for internal. A breach in one of the heat exchangers that can mix the coolant with engine coolant or the domestic water supply.
Get a radiator pressure test set up and begin there.
Thanks for the replies, I will start checking things out as suggested.