[Sven7]

If you're really going for "MAX" mpg and the truck is not worth restoring, you might see if getting some skinny, high offset wheels and skinny tires will bring them inside the bodywork far enough that you could chop off the wheel arches to have a nice, smooth body side. This would make it really easy to mount a wheel skirt. I believe early Mk1's had 4.5" wide wheels with something like 45mm offset. Poke around on your local VW forum or VWVortex to see if you can score some. Mounting aero discs on them wouldn't be a huge issue. Or just get teardrops, as they're about the most aerodynamic wheel you can buy for a Mk1, and would probably be a solid choice despite being about 19lbs a piece.