Aero for large vehicles...
 

https://www.unicell.com/pdfs/AerocellChevUCAC.pdf

"Since introduction, highway users of the Aerocell have consistently reported
15-20% fuel savings compared to a conventional body on a cutaway chassis."

https://www.unicell.com/bodies/bodiesMain.html

I'm going to use that design as a guide to make one...but doubt if I can manage the smooth flows....mine will be more angular.

They need some airtabs at the back???

be nice if they could mold air tabs into the body - would like to make a rear spoiler like that on my xB and just bolt it on.