Replacing Refrigerator, vents and wiring questions

The existing 12v battery charge line should work fine on the road. Trailer battery may not be full charge when you arrive so plan to plug in or start the generator on arrival.

I would plan on 500+ watts solar and 4+ batteries for dry camping. You will still be running the generator a bit. Most use a 1000w sine wave inverter. You can get a small transfer switch that plugs into the inverter and connect to the existing fridge branch circuit.