Somewhere in your RV there is a NEUTRAL to GROUND short. It could be anywhere.
Disconnect the RV from all power. Remove all NEUTRAL wires from the buss bar in the breaker box. Plug back in. If it trips, the problem is between the Surge Guard and the breaker box.
If it doesn't blow, disconnect, reattach one NEUTRAL wire, reconnect. If it blows, that is the circuit with the problem. If it doesn't blow, repeat process till it blows.
When it blows, trace that NEUTRAL to see where it connects to ground. It could be in a stripped/pinched/punctured wire, an outlet, an appliance, anywhere.