Post #2 is correct, exterior walls are not hollow and would be practically impossible to get a "fish" through to pull wires. Possibly you can drill straight through to the inside, where you could come into a cabinet (hidden) and then pick up a 12v feed from there.
George R. - Fulltiming since January '03
2007 Newmar Mountain Aire 3991
2012 Chevy Malibu LT1