I think if you do a search you will find that the predominant areas of thought are to replace the cooling unit with the Amish or go residential. As you mentioned, the Amish suppliers do not seem to make a replacement for your larger Norcold.
While many have chosen many residential alternatives, the one that seems to be mentioned most frequently is the Samsung RF197xxx (which has now been replaced with the Samsung RF18xxx
). This new unit may just be what you need since Samsung claims it uses less electricity than the previous model. The only thing about this one is whether or not it will work with a MSW inverter. (The previous model would.)
The good thing about the Samsung is that folks with the standard 4 6-volt house batteries seem to get along just fine with this unit. So, your concerns about draining the batteries seems to be mitigated with this unit. (Some report running the generator an hour in the AM and an hour in the PM to keep things charged up. This seems to be adequate to keep things in order.)
I would certainly be leery of replacing a cooling unit that had only lasted 6 years.