I would go the
whole way- further than anyone here has gone before (with a pickup).
Since you can weld, here's my plan
Start with a small pickup with a manual trans. Convert it to electric. Remove the bed and build a custom rear end that tapers in a teardrop. Narrow the rear axle to fit within this teardrop. Seal up the bottom, the front, all the seams. Moon caps on the wheels and front wheel skirts. Wheel fairings/strakes. Skinny LRR tires.
If you started with a 2WD Nissan Hardbody you'd probably be able to get high 30's mpg. But with electric, you'd pay a lot less for the fuel!
You'd end up with something similar to this, with two rear wheels...
...but with correct angles to avoid longitudinal vortex formation. Read up on aerohead's posts in the Aerodynamics area of this forum, as well as the current CRX HF trike project, and buy Hucho's aerodynamics textbook and Leitman's
How to build your own electric car book. Then buy a truck and start working!
(most of us dream of having an opportunity like this)