Here is a typical 30AMP Electrical Block Diagram that might she some light of what does what...
Your Trailer have two POWER DISTRIBUTION CENTERS one for 120VAC and the other for 12VDC...
The basic concept is Shore Power or generator will run your 120VAC Power Distribution where a 120VAC Converter is used that will produce 13.6VDC to run the 12VDC Power Distribution side. Your battery is direct connected to the 12VDC side and when you are plugged into shore power or generator your battery should also be charged while you are doing this. Without Shore Power or Generator then only the battery side is working feeding the 12VDC side of the Power Distribution side.
Google image
If you want to run some 120V Outlets etc you will need to install a Power Inverter to run from from the 12VDC side to produce 120VAC. I do this all the time to run a small 'Pure Sine Wave' 600WATT Power Inverter from my multiple battery bank and then I run two 120VAC extension cords from the Power Inverter to a couple of locations inside the trailer. Home entertainment and a couple of lights/fans etc maybe a power station to run some battery chargers for laptops etc...
The battery Bank will need to be upgraded to more batteries to run the Power Inverter. I did just fine with a 255AH battery bank for a few years - finally bit the dust just a couple of seasons back after being initially installed in 2009. Then when the batteries get down to around their 50% charge state you have to come up a way to recharge them back up to at least 90% charge state otherwise it will do damage to your batteries... I use a 2KW generator to only run my Converter/Charger unit to recharge my batteries which takes around three hours of generator run time to go from 50% to 90% charge state. Not all places will allow you to run the generator especially after dark.
Got to do some planning here to get setup for what you are wanting to do... You just can't show up and snap your finger and it all works... After everything is planned and gets installed then it is all second nature camping off the battery system OFF-GRID...
We camp more OFF-GRID with our batteries then we do at regular camping spots with electric hookup...
Roy Ken