NP Di-D Pajero Dual Battery Setup

Has anyone had any experiences with installing a second battery in an NP Di-D Pajero. If so just wondering where you put it, and what size battery you were able to put in.

I am looking to put in as big as battery as possible, so I can run the fridge etc when I go camping. I know with the petrol variety they fit a smaller battery between the original battery and the firewall and use this as the main, then put a larger battery in the original position for the second battery. However, I'm not to keen to swap the batteries over like this with the diesel.

Thanks