Were all the other AC breakers (in the camper) off, when you islolated the main as the problem circuit? If they were on, the problem could be in one of them.
I too, think it's a mouse issue. They like that plastic covering from romex wires. Look for chewed wires. Disconnect shore power and look everywhere you can see any AC wiring. Including, behind the converter. You already know, the short is not between shore power connection and camper's power panel / converter.