I would recommend a wind deflector, particularly if you have a shell and can mount it back close to the front of the trailer except that I don't have the inclination or energy to argue about how well they can work. For the record we consistently got an additional 1.5 to 2.0 additional mpg towing a 5000# TT with my F-150 SCab. PM me if you would like details.
What will work without much argument is to simply add a Scan Gauge and then pay attention to what it is trying to teach you about fuel economy. Most folks find an additional 8 to 10% improvement but this will involve backing off that right foot which some folks are loathe to do. Bottom line it is always going to be an 8000# brick and the wind is not your friend. :S