In the case of reverse polarity it has to do with the power being transferred by the ground wire and not the neutral. This can be completely or partially and this is usually the term used in marine applications and is actually a ground fault by definition if you are not on the water.
This unit is mainly used to detect a problem in the wiring from the marina dock and not within the boat, although it would do that as well.
The inverter should have it's ground connected to the RV ground circuit and the neutral should be isolated from that ground. The inverter would be connected to the output neutral and hot from this breaker.
The reverse polarity breaker you have is mis-applied in this case.
That breaker is designed to meet the requirements of the USCG ABYC and others.
The RV must meet the rules of RVIA and the NEC.
Are you wiring a boat or a trailer?
You would do better to use a GFCI, but here is a diagram for wiring from Paneltronics.
Reverse protection circuit breaker.pdf
You should probably feed the inverter from the load side of this breaker if you keep it in the circuit.