Ranger connecting to Drifta DOT batteries etc


New Member
Hi everyone. First timer on here - just picked up Drifta DOT second hand and working out how I get my Ranger setup to have a good camping battery setup for both car and trailer.
No setup in car at all - blank canvas.
Attached is a picture of what is the go in the trailer - it has a 7pin and Andersen at hitch.
The battery charger (Bottom left) has a connection to connect to mains. I do not think that the andersen car plug wiring goes through this - unsure of what the actual setup is with wiring from car.
In the picture - I am holding a connector for an additional water pump which goes in 12v cigarette socket.
Mid left = fuse box
Top left black box = controls for actuators for rooftop camper lift
Top left white box = water tank level.
My question is - what is the best setup to get for the car?
We will likely run a fridge - but again happy for this to just be wired in (with relay to ignition to switch off with ignition - prevent draining the battery) rather than have dual battery setup. Have been told that to get a DC charger unit in the car will make the job expensive (~$1400).
Getting a bit lost looking at circuit diagrams etc. just too many options.

Any advice is much appreciated. I want to try and get it right the first time - rather than have to have a few trials