Hi,
Yeah, I'd like to know the answer too! I would think you can - it's just a battery in a box. Should be right with an isolator and the correct wiring. I don't know about the DC/DC part. Someone will know though! We have just used our Arkpak to run the fridge and charge the mobiles/tablet, etc. They are a great unit!
We just use an Airflex (flexible 2kg solar panel) that can be mounted on the Pioneeer Roof Tray. You could use any folding solar panel and charge the car's battery up when you reach camp if you wish.
Cheers,
Sally