Seems like an awful lot of unnecessary re-wiring to me. You didn't specify what type of inverter you are using. The first problem I see is the Romex, which is fine for a house but NOT for an RV. Yu should be using nothing less than marine grade stranded cable for any re-wiring. I really don't care what Airstream uses, as I have spent unnecessary hours tracking down breaks in solid copper wiring caused by work hardening in moving vehicles.
If you go with a quality 2000 watt (or 2800 watt even) inverter/charger system (like the Magnum MS-2012 or MS-2812), you can dump your worthless OEM converter and charge your batteries properly with temperature compensation and full adjustment for size of your battery bank and type of batteries.
You can then have up to 2- 30 amp output circuits that will then run everything in your trailer with no additional wiring, using all of your existing circuits and breaker box. This happens because the inverter/chargers have an internal transfer switch that will automatically
do the switching for you. Just a bit of minor re-wiring is necessary.
A much simpler, more elegant solution to your re-invention of the wheel....so to speak!