To continue the discussion from Street Rod Jim's build thread, I think the root cause of the problem comes from the gaps between the door and the top at the ends of the doors allowing air in and pressurizing the interior. There is a need to have some kind of seal at these points to minimize air infiltration. The outlet vent for the truck mentioned would be a big help I believe in addition to a seal of some sort. I've been thinking about this for some time when I realized these areas would be open to outside air. If I figure out something I'll let you know or if someone else does, let us know. It might be awhile because I'm not to that point but others are there or beyond. It's something that can probably be fixed after the fact.