I'm not convinced that going small is required. Last summer I made a run from Rocket City(HSV), Alabama to Road America, Wisconsin with my 16 tandem axle enclosed trailer behind my F250PSD with 845 Lance Lite. I maybe was down 1/2 to 1 mpg over TC solo. I didn't set any speed records but paced traffic well enough. (GVW police need not comment,I know!!)I figure the trailer was "drafting" and the slight step down from TC to trailer in height made a better transition for the airflow. Got worse mileage on a trip to Sturgis sans TC so the trailer/TC combo may be synergistic. I'm seeing more semi's with an aero package (skirts and tapered false rear doors) so the extra length may not be a big issue if you can "taper" the drag.
