I want to put an A/C plug at the rear of my vehicle to connect to the RV so I can use small appliances in the RV powered by both an Inverter in the vehicle and using the plug in block heater system for external 120v. While running down the road in cold weather I can power a small wattage space heater in the RV (during cold weather) or to run <1500w power without having to plug in the RV. Basically using my Diesel as a generator. But when I'm at a campsite I want the system to switch so when I plug in at an electrical site, plugging in the engine heater will also run the RV. The engine heater setup has a standard outside utility box with 4 plugs for the heating devices so I could easily just run an extension cord from that through the vehicle to the rear but that wouldn't power the RV while going down the road.

I'll add more to this description. The challenge is I need to switch power between external and internal and can't have backflow to the heater coils as that would overheat my diesel while it's running down the road. I'm not sure if there's a power relay or a transfer switch or what would work best and how to wire it.