I have a few comments for you regarding truck aerodynamics. I have been involved in the development of virtually all of the aero add-ons used today. The work was done in the wind tunnels of the National Research Council of Canada form 1976 untill today. Current trucks have much lower fuel consumption than several decades ago. The largest contributor to this improvement has been aerodynamic improvements. I would recommend both boat-tails and trailer skirts for your fleet, assuming that you already have the cab-mounted aero packages and cab extenders. For more info download the Society of Automotive Engineers paper SAE 2003-01-3376, entitled "Truck Aerodynamics Reborn – Lessons from the Past" by Kevin R. Cooper, Aerodynamics Laboratory, NRC Ottawa, Canada. For more info contact
Kevin@CooperAero.com. Good luck.