Alittle reality came to me as to heating/cooling these GMCs. It's a lot of cubic feet, and mass for a basic van system to handle. For medium heating, or cooling. We have a tarp that we hang across, at the side door. For real cold driving. I turn on the furnace. For real hot driving. Run the roof A/C. With Linda in her wheelchair. She can't ride up front. Thus I need to heat/cool the back more completely. When we leave Iowa in Feb/Mar. The GMC is inside at 70. We drive out the door. And don't stop till we hit warmth outside. Thought about adding more heating/cooling units at the rear. But what we're doing now. Works. Bob Dunahugh