I agree with "Bill.Satellite" on this one. Even though you say you run your generator or connected to shore power at all times, there will always be a situation that pops up where generators are restricted, broken or inappropriate. We run our generator to cool the coach when driving in weather above 90 degrees, but that's only a few trips a year. The rest of the time there is no need to run a generator.
The price of a new Norcold is about $3500.00. The price of a new residential unit is about $1200.00, plus install if you can't do it yourself. That stills leave you some money left over to add a small inverter. This will also stop the constant turning on and off of the residential unit.