What @TheSpareTir3 is thinking is trying to help you improve the efficiency when dry camping. If you wanted to run all the outlets and AC etc, you should get a inverter charger like the Magnum or Xantrex lines. The reason is even if you get new 6v batteries you need a new multistage charger because the onboard will take forever to charge and never equalize or desulfate. This adds easily $250 to new batteries.
If you want to start the AC or microwave from a small inverter generator you probably need two in parallel because of the peak power of these devices. However most of the time you don’t need that much power.
This is where the generator assist inverter chargers are the way to go. The bridge the gap by assisting the generator when it can’t make up enough power by borrowing some power from the batteries. Then as the load decreases it recharged the battery. This fills in the peaks and valleys of power usage, means you don’t need the second generator. Use less fuel with the one you have, less maintenance, noise, pollution etc.
As for a charger they are multistage and automatically reduce charge as your load goes up, something onboard can’t do.
For wiring, they are added between the shore power cord and the fuse panel. Means it can in theory power anything in your trailer.
Victron another manufacture made a great white paper on this topic - https://www.victronenergy.com/upload/documents/White-paper-Using-the-MultiPlus-to-reduce-operating-cost-of-a-generator-EN.pdf