External Generator use on Class A

Most Xantrex inverter/chargers allow you to turn off the charger. Check your owner's manual. Basically, you can turn the inverter off completely and use your exterior generator as shore power. You can then go to your main circuit breaker panel and turn off every circuit in your coach if you want to isolate the large power consumers. The you can switch each one on to find the circuit that is overloading your generator. The microwave is a large draw at 1500-1800 watts. It is doubtful that any roof top AC unit will work with a 2000 watt generator just because of the starting surge. The rest of the draw will depend on what you have plugged in to the various outlets.
Keep in mind that certain things in your coach must have the 12 volts, such as your various detectors, and your lighting. This means that with the charger turned off on your inverter, your batteries will eventually run down.