Rather than a long nose cone, it's the rear end that needs the attention.

A collapsible colluder cone is what is needed, and gains in the order
of 15-25% in MPG(hwy) would be possible with it based on what we could
expect to see in drag reduction.  It's not the piercing of the air
that's the real problem as much as bringing it back together smoothly
behind us, besides having an attachment behind the van is much more
practical as well.  The top half would be transparent, the bottom half
rigged to carry light bags and light luggage if desired. Clips on in
about 5 minutes like an old style bike rack. If we did end up building
a prototype and it proved close to the expected numbers, I wonder how
many people would be willing to run one?

Jim Akiba