I had a setup like that on a pop up a few years back. The converter will charge (maybe over charge) the battery. A converter makes 12 DC volts from 120 volts AC. I mounted a battery box on the tongue area arid wired it up like the diagram shows. The converter is not regulated and will most likely cook the battery if given too long of a charge. Since we never had hookups, it was not a problem. I would charge the battery with a regulated car charger after a trip. The only power we needed was to the water pump and one light. We could go weeks without a charge.
WBCCI President 2016-2017