I'm trying to decide whether to change em all out to 120v and run some wires or add a battery on the tongue and mount a battery charger inside to keep the battery full when connected to 120.
You will need a battery somewhere on the trailer to make operable the emergency break-away part of the braking system. Also, most trailers require 12V for furnace and fridge operation, as well as operation of the water pump. Using a stand-alone battery charger is OK but you may have a 12V converter installed already. That supplies charge current to the battery when connected to shore 120V. The charging section is below the circuit board and 12V fuse panel, if so equipped.
I lkie 12V for lights as there are many choices for 12V LED bulbs and they draw very little power. They're also always available if my batteries are charged.