how to get cable from engine to cabin

I want to put a 2nd battery in the cabin to charge from the alternator and isolate manually with a 1-2-off isolator, to keep it simple. I only want to power an electric cool box (fridge to come later) and 1 LED light. What's the best way of getting the power through from the engine bay to the cabin.
I have a 2003 Patrol GR 3.0l auto.
Thanks.

Just use the main wiring loom that in the engine bay on the driverside , once in use the bottom door frame covers driverside that has wiring channel already and remember battery for cabin use a AMG or better, not a normal car battery. regards Alex

I ran my 4awg cable through the passenger side firewall using an existing grommet (mine is a 2004 GU III TD42TI).
Have a look under the bonnet on the firewall for some exisiting black rubber grommets, either on the passenger side or driver's side, there should be locations you could use on either side.

Thanks, my intention is to use a deep cell maintenance free of around 100ah. I'll have a look for the grommets.

There is a large grommet on the opposite side of the car to the steering wheel ( regardless of left or right) it is the grommet used for the steering column on the other side of the world. It is perfect. Find where the steering column would be if it was in the passenger side of your car. You are in business.