If you have a lighter/power socket that is hot off the CHASSIS battery all the time (Dodge/Freightliner/Benz) Sprinter is this way, then go to Ebay and search for VW solar panel. It is already set up with a plug to fit a lighter/power socket, and will charge the chassis battery if it can get enough sunshine. Most are about $20 or so. VW put one in each car shipped, the dealer employees stole them, and sold them on Ebay. I don't think VW uses them any longer but they are still out there. I doubt very many new VW owners were ever given theirs, and probably didn't know they existed.
Charles
