How much do you actually plan on driving your truck? The OTR trucks and trailers you see with the aerodynamic kits are rigs that see hundreds of thousands of miles a year of interstate highway cruising. For rigs that get 10-15 (guess??) mpg of expensive diesel, the single digit improvement in MPG is real money to them. It may not be worth the expense, effort and ugliness on an occasional use antique.
Is fuel efficiency that critical here?