You could do it that way, others run it inside the chassis, and a lot run through the sills inside the car.

There's heaps of info on this site if you look at dual battery systems.

I did it in my 120 through the chassis rail. I have 2 x Andersonville in the cargo area and 1 x Anderson on the tow bar all supplied from the one VSR under the bonnet.

A few posts to look at, if yours is a 2.8 there are another couple of threads.

http://www.pradopoint.com/showthread...-Battery-Guide
http://www.pradopoint.com/showthread...ack-of-the-car
http://www.pradopoint.com/showthread...ry-in-2012-GXL
http://www.pradopoint.com/showthread...-down-the-side
http://www.pradopoint.com/showthread...mart-Solenoids
http://www.pradopoint.com/showthread...y-Cable-Length
http://www.pradopoint.com/showthread...ons-and-advice
http://www.pradopoint.com/showthread...gers-Which-one

My set up is a little different. Manual circuit breaker next to the main batter with 6B&S cable feeding a BCDC1225 in the back next to an AGM battery in a dedicated box. Solar in feed via a changeover relay. Wired as per Redarc site. Auxiliary loads include fridge, voltmeter and charging outlets.

I am soon to run power to the towbar to supply power to the camper. For this I will fit another manual circuit breaker to a Redarc SBi12 then along the chassis to an Anderson plug mounted on the towbar. This way I can isolate that feed when the camper isn't connected. The camper has two 105 AH AGM batteries and a BCZdC1240. The infeed from the car in the camper is connected to the trigger wire for the changeover relay so I need a voltage sensitive relay under the bonnet.

I haven't started this because I will need to TIG weld a bracket to use under the bonnet which will have the two circuit breakers and the SBi12 and I have only just picked up a bottle of Argon.

Some pics of the first part in my build which you can get to through my signature link.

This is my set up. No volt drop in these cables. Cables inside chassis rails.






25mm from main (aux) battery to rear of car with 100 amp circuit breaker.
Second circuit breaker for spare next to winch.
From the rear fuse box have 16mm cable to trailer anderson on tow bar, the rest are 6mm for fridge, codan, solar (separate anderson on tow bar), inverter and a spare.

Rusty.

If you are using a rear fuse box avoid the ones that have the push on crimp joint and go for the screw in.

i ran 2 cables.
One along the chassis for the Anderson on the towbar.
One through the firewall into the rear.

Cheers guys very helpful thank you will post pics when I get around to doing it