Here is a TYPICAL 30AMP Wiring configuration showing what is controlled by the 120VAC and 12VDC Power Distribution Panel...

The basic concept for the RV Trailers is to be able to work from Batteries only with the bare necessities or from the 120VAC Electric Pedestals running all of the appliance and functions..
when camping off the power grid on batteries only you can add an INVERTER connected to the battery bank to run many of the 120VAC items. The Battery Bank would have to be many batteries to run the whole trailer.
With this in mind when camping off the power grid alot of folks will just run the 120VAC Home entertainment items from a smaller INVERTER. The rest of the bare necessities will run directly from the 12VDC battery bank.
You have to plan everything out to be successful camping off the power grid running from the battery bank.
LARGE capacity INVERTERS are very battery hungry...
Roy Ken