CONverter?
Yank the shore power connection. Disconnect the BLACK 120 volt wire connected to the converter where it is marked LINE. Tape the end of the disconnected black wire. Connect shore power. Does the GCFI fault? It's silly to connect a converter to GCFI. Methinks there is misdiagnosis going on here. Never have seen an RV use a decent GCFI. And I would not be caught dead with a Leviton. Go to HOME DESPOT and forget the bargain GCFI units. Purchase a 20-amp rated quality brand. Install it then light it off to test.