There is a unit called DC Airco. It is a roof mounted, 9000 btu,
12 volt unit manufactured in the Netherlands and marketed By ESPAR Products. We have installed a couple and have had good results. We isolate two deep cycle batteries from the starting battery, then while the van is running down the road, your charging system recharges the DC Airco batteries. Call us, we can help. 800.837.3900