[spacemanspif]

It would probably be easier to rig up a solar charger above the "battery box" in the bed to tend the batteries while the fans are not running and while the truck is parked, parking outside would be best, of course. But on a truck that already runs dual batteries why would you want to add more? I would be a damn shame to be stuck in traffic with the AC on when your batteries die and the fans cut out. Running them off the engine's electrical system would be a safer bet since the fans will keep running as long as the alternator works. With an engine putting out 800lb-ft fo torque, is the extra load on the alternator going to make that big of a difference?