I would begin by checking for AC power from the campground. Does the converter make a hum sound? Does the air conditioner fan work? Either indicates AC power present from either the campground pedestal or generator.
Maybe something really bad happened to the battery and blew a fuse in the converter. It might be best to disconnect the battery while troubleshooting and hopefully charging that poor battery with a borrowed charger. Check for 12 volts at the indicator lights or meter, 12 volt lights, furnace fan working. Put a 12 volt or higher voltmeter on the battery cable with other probe to ground. As mentioned it should show at least 13 volts. Failure indicates trouble at the converter or AC power to it.
To check a fuse you almost need the voltmeter to measure voltage while the fuse is in place, from one side of fuse to ground, then the other side to ground. If 12 v on one side but not the other, the fuse is blown. If no voltage on either side, look for a main fuse blown or a breaker tripped.
Don't hesitate to ask another camper to help. I would be thrilled if someone asked me.