question

I'm not sure I'm understanding your connection method but there should never be a fuse in the safety ground circuit. That path needs to be able to carry all fault current from the short back to the service entrance.

The inverter was a COMMON safety ground connection (labeled PE) for input AC, output AC and chassis. The incoming AC safety ground as well as the outgoing safety ground to the RV outlets and the RV chassis should all be connected to this common safety ground path. It is the incoming NEUTRAL connection that opens when the unit is functioning as an inverter (not using the AC input). The output neutral then connects to the safety ground. This "ground relay" then provides a fault path for inverter supplied power in the same way that the neutral to safety ground bonding in the service entrance panel does for a building.

I believe Victron recommends an RCD on the inverter output since the input RCD won't detect a ground fault when the inverter is inverting (not using the AC input). At the very least, an overcurrent protection device should be used to avoid inverter overloads. Local codes would be a good source to check for what's needed.