Everytime some one mentioned BATTERY ISSUES it is always a good idea to check the battery installation...
I always look at the battery case and look for the word 'NEG' or the symbol '-' and make sure this is the terminal that goes to frame ground... This is regardless of the battery cable color...
The RV trailer should be using the BLACK and WHITE colors where white is the NEGATIVE FRAME GROUND cable. However since this is a battery installation sometimes you see those wires have been changed to the automotive colors of RED and BLACK where BLACK would be the NEGATIVE cable color. Very easy to get it hooked up backwards which blows inline fuses and one thinks the converter is not working. Another quick test for the converter is to not have the battery in the circuit and connect to shore power. If the ceiling lights work normal then the converter is working. Both the Converter and the Battery feed the same point on the 12V Power Distribution Panel so that the trailer 12V items can operate form shore power or off the battery. When on SHORE POWER than this connection also charges the battery...
Something like this at any rate haha...
Roy Ken