If the main breaker in the RV is off, the fault would have to be before the breaker (or the RV's breaker is dangerously malfunctioning, which is not very likely). That generally limits things to the entrance cable, the EMS system if you have one, and the generator transfer switch if you have that.
The converter/inverter should be on the other side of the main breaker. Perhaps a large whole-house sort of inverter may be wired with a transfer switch before the main breaker, but I wouldn't think that's especially common.
If you have a multimeter, check the resistance between the various prongs of your RV power cable with the main breaker in the RV off. There should be an open circuit, or very nearly so if you have an EMS, between any and all of them.
