On the 120v ac side: If you are going to run AC/ firing pan/ coffee pot/ arc lighting/ 2000-watt stereo/TV/DVD/VCR/swimming pool heater and stuff. You will need a circuit breaker box just like the one on the farm. But if you are looking at one outlet for the battery charger and one outlet for the galley, for use with the coffee pot or firing pan, not both at the same time. Then wire it from the shore male plug to a GFI outlet at the battery box. Then add the galley outlet after the GFI so both are Ground Fault Interrupted protected. The law wants the ground wire to the frame of the trailer also but I don’t like that, for a simple AC power system. If the shore power has an open ground some place one mite get a shock from touching the trailer frame. Just make sure your ground wires are wired to both outlets and the plug going to shore power. Do an inspection of the shore power outlet with a tester to make sure it is wired right. You can bye an AC outlet tested at any electrical supply/hardware store or Home Depot. There cheep personal protection.
12v DC side: You do it just like down on the farm. A main fuse and each circuit has it’s own fuse. Else you will have a flaming tear going down the road. That is literally not a British slang word. Batteries will supply more and more power to a short. Where there is smoke soon there will be fire. It’s hard to put out fires at 65 MPH.