I'm sure there's plenty of info in amongst aux battery threads here, might take a bit of searching but there have been quite a few posts relating to the current model.
On ours I installed a Piranha 140a battery isolator and this fitted neatly down beside the main battery and cables to the back went out under the carpet. The second battery in my fridge and drawer module is fed by another cable with an anderson plug connecting to a DC-Dc charger.
For info on trim removal look here...
http://www.wk2jeeps.com/wk2_interior_trim.htm
If you haven't prowled around the wk2jeeps site then you have a lot to look forward to.
john