Some more light reading..
http://nparc.cisti-icist.nrc-cnrc.gc...3-9658934e59e0
Of note, looks like a trailer fairing would be beneficial..around 1.5% aero drag reduction (.75% fuel economy)
also, underbody plates between bumper and front axle, combined with TOP of chassis (behind cab) plates to prevent air entering into trailer gap ..around another 1% economy saving..
Would have to make the underbody plates pretty substantial however..possibly alloy checkerplate with a lot of bolts..otherwise a kangaroo will rip it off in short time..