This is the basic wiring configuration for a 30A Wiring Configuration...

As you can see here every thing revolves around the 120VAC Power Distribution Panel where the Circuit Breakers are located and the 12VDC Power Distribution Panel where all of the ATC TYPE Fuses are located.
The 120VAC Power Distribution panel is powered by the Shore Power Cable or Generator and the 12VDC Power Distribution Panel is powered by the 12VDC OUTPUT leads of the Converter unit and the 12V Battery setup.
When running on Shore Power or Generator the Converter is also a DC Charger unit to maintain the Battery operation. This is why you see the Converter also called a Converter/charger unit.
You can see at the bottom of this block diagram where when operating without Shore power or generator the BATTERY can also provide 12VDC power to an optional Power Inverter that can provide 120VAC Power for such things as 120vAC Receptacles or other 120VAC Appliances that may be plugged into these 120VAc receptacles. These are OPTIONAL for the most part but some of the newer high-end trailers may have this Power Inverter built-in with auto switchover circuits...
This is to give the basic concept of the 120VAC and 12VDC Power in the RV units is managed...
The original RV Trailer concept was to have all Installed appliances functional when on Shore Power or Generator but only the very necessary functions only available when on BATTERY only. The necessary functions being run off of the 12V battery setup only includes lighting, limited entertainment setups, with cooking and heater features being run from Propane energy.
To have all of the installed appliances functional without Shore Power or Generator would require an optional POWER INVERTER setup to produce the required 120VAC being run by a very large battery setup and a robust way to keep the multiple battery bank charged.
Lots of folks do not know the difference between the Installed CONVERTER/Charger unit and the optional POWER INVERTER units.
Hope the simplified Block Diagram helps identify the 120VAC and 12VDC Power Distribution features of the typical RV units.
Roy Ken