This is a typical 30AMP Electrical Configuration setup showing the 120VAC and 12VDC Power Distribution Panels and what they can control.
Photo from GOOGLE Images
The basic RV TRAILER concept is to be able to operate most of your necessary lights and few appliances from 12VDC Batteries when camping without 120VAC shore power connected.
When you are plugged into 120VAC shore Power you can then operate all of your Appliance systems.
You can also operate a few of your 120VAC Appliances when camping off the power grid by adding the correct sized INVERTER unit but must keep in mind the INVERTER is very 12VDC Power hungry and will require many batteries to operate the bigger wattage 120VAC items.
Camping off the power grid does take good planning on beefing up your 12VDC systems to be successful for longer term camping.
The RV camper is an amazing concept.
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS