Great news, everyone!
Poking around in that old thread I found, downed, and re-upped the picture of the Vanagon that was lost to Photobucket's [expletive deleted]. I renamed it 'boat tail box cavity'.
Notice the solid floor. This informed my design for a retractable boat tail for the Type II.
I got sidetracked. I was looking for a picture of Morelli's Urban Car. Before EcoModder I thought the most aerodynamic termination was a 45° chamfer, like the Urban car. (I'm thinking of the profile drawing with the wake in yellow) I'd hope it would be in this massive data dump from 2016:
Body plan taper and drag. But I did find this. I find Mair more helpful than The Template.
Has Photobucket un-borked itself?