Well the rear certainly does drag along a lot of turbulent air.  But the
front end starts all the turbulence, and once it becomes un-attached from
the object, it hardly ever goes back into a smooth, linear flow, which has
the least drag..  So the air probably is pretty disturbed all along the
sides and roof.
Under, you have the boundary layer to consider, probably beyond our
discussion here, though a belly  pan would do wonders, and it wouldn't make
the Vanagon into a Frankenstein with visible add-on body work.
  For the rear, perhaps you could fabricate some kinda "Space Case" type
luggage compartment that might fill the vacuum behind the rear...Or a slick
receiver hitch cargo/aero compartment AND another mounted right behind the
rear glass..The  least that would give you would be some "free" (no negative
aero consequences) carrying capacity for bulky items..
  You might get some small improvements with flaps and spoilers..but that
would take real science to see if indeed it actually worked...The wing on
the 928 rear hatch was just such a beastie...not a wing for downforce, but a
spoiler to help release the air and reduce drag..The 928 also came with full
belly pans...but like everything on that particular car, they were
over-engineered and total pain...it took an hour to change the oil because
of those belly pans..
  Don Hanson

----- Original Message -----
From: "Alistair Bell" <albell@uvic.ca>
To: "Don Hanson" <dhanson@GORGE.NET>
Cc: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, July 28, 2007 11:00 PM
Subject: Re: Some aerodynamic ideas..

> Don,
>
> good points but what about the rear end? In my opinion its the
> draggiest part of the beast.
>
> Alistair