There is a automatic transfer switch, about $75 for a 30 amp single pole breaker. You might want a 50 amp two pole breaker that is a bit more expensive - say $120 to $150. With it, you can also control a 20 amp breaker to feed the battery charger while on shore power or generator, but leave it off while on inverter power.
You can install a new 20 amp receptacle to plug in the converter to. The shore line and generator can go into the transfer switch via your stock cord. Then the inverter can go in the "Gen" side, that goes through without the relay being energized. (this saves power). With a two pole transfer switch, have the "Hot" go to both inlets on the "Shore" side, and one output to the RV panel, the other to just the converter new receptacle. The other input goes to the inverter, and do not connect to both sides, so it will not power the converter/battery charger.
By the way, you can use the circuit breakers as switches. It is not the "Best" thing for them, but especially while not under load, it will not harm them. So if the A/C is not running, it is fine to turn on the CB and off all you want to.
Fred.
