Ron, Of course most modern class 8 trucks have side fairings to help control the air getting under the truck, and as has been mentioned already, a lot of trailers now have added on fairings from the landing gear to the back wheels.
So, I suspect a travel trailer/pick up combo could benefit from similar add-ons. And don't forget that many of the days we travel, we experience winds that come at us from an angle, so at least some of the air we are trying to slip thru is swirling in to one leading corner or the other of the trailer.