That gets me thinking: If the cab-top diverter was hinged at the location of the 5th wheel with a parting line that was centered on the hinge; then as the cab's curved top pitches relative to the van, it could maintain that minimal gap.
so much aero, so little time:
http://justacarguy.blogspot.com/2016/05/om-empahasis-f-g-it-looks-like-someone.html
The Aztek didn't get any respect, but the roofline is all templatey. I went as for as checking availability:
https://www.autolist.com/pontiac-aztek#radius=any
Three available instate for $4-6K. I'd spec a body colored grille block, like the VW Nils [bumper]...
...and then fill the upper 'nostrils' with LED DRLs. They look a little bottom-heavy, so everything below the mid-body crease should be satin black.