What are you planning on experimenting with? If it's your 38, I don't really see the point. First off, the draft tube needs air acrossed it to function properly. Secondly, the the pre-war trucks are about as aerodynamic as it gets with there smooth body lines.
On a pickup, maybe an under bumper spoiler and some skirting under the running boards may help, but I can't see a significant increase in economy.
