The Norcold broke (again) and I am going with a Residential.

I'll point out that the Norcold is twenty years old- I can guarantee that a residential model will not last anywhere near that long when used in an RV.
Just spend ~$100 on a Dinosaur board and be done wit it. Other wise, in another 20 years tell us how much you have spent on batteries, inverters, refrigerators, etc.