We used a mechanical dehumidifier in our old JayFlight and now the same one is installed in our new Greyhawk. I run the heater to keep the temperature above 50f. I have the dehumidifier set to its lowest setting of 35% RH and to automatically shut off when the set point is reached. This setup kept the JayFlight water free all winter for more than 7 years. This is the only way to go especially if you use your coach in the fall, winter, spring when it is wet and humid. I learned this the hard way when we were camping and got caught in a snow storm. We had the heat on and 5 people in the trailer. We had so much humidity it was running down the inside walls. Now we don't even have problems with foggy windows except at the cab section of the motorhome.
2004 Chevrolet Silverado 3500 LT with a 2004 Jayco JayFlight 29BHS
2014 Greyhawk 31FS with a 2007 Tahoe toad
2014 Thor Palazzo 33.3 with a 2007 Tahoe toad