I use a dual battery system in my 2012 Laredo, to power a 12v fridge and other accessories.
I fabricated a slide in module for the cargo area and when going away the module is slotted in, with the fridge, the 80AH deep cycle battery, table and chairs and lots of other stuff.
Like Peter T, i use a DC-DC charger mounted on top of the battery box, and connected with Anderson plugs and 6 B&S cable back to a Piranha DBE 140S battery isolator mounted down beside the main battery.
I installed the Piranha in the first few days of ownership and it has remained connected for 20 months and 53,000K with no issues.
The module has been in and out probably 10 times and each time the setup works perfectly, charging and maintaining the accessory battery. Some pictures in this thread: Secondary Battery Ideas!!!
A number of Aussie owners have installed similar setups with different VSR units.
The only issues I have read about have been with VSR units that have the cut in threshold too high to be compatible with the WK2 system voltage. Fitting programmable VSr units have solved that issue.
With the proper research and components you'll be able to enjoy cold beers on the track.