I saw your posts about using the D Piller floor holes as vents in your Transit. I was going to do the same thing.
I'm not quite sure what you used though. You mention you used some type of duct.
Was this from the bottom opening to the 'main' opening about 4ft high in the pillers?
What did you do to prevent 'leakage' through the other holes, to get most of the flow through main part of the van (above the bed), or did you now worry about that?
Also, how did you block airflow on cold nights, or prevent exhaust entering the cabin during a drive (Although I think I read you have not noticed any issues with exhaust yet)? Do you have something to close at the main entry way, or do you close it from underneath?