I need to wire an Anderson plug to the rear of my 2014 ST Wagon, It will be connected to an AUX Battery (when I fit it)..was wondering what is the best route to run the wiring to the rear...

Can I run it through the Chasis rail, or does it need to be run on the outside of the rails?

If I use some twin core 10mm? should I still cover it with that flex tubing stuff?