My set up will get 10 MPG with a bit of wind behind me. Average about 8 MPG, only 6 MPG with a strong headwind. My V front trailer gets about 1 MPG better than my flat front three 26' SunnyBrook trailers; and that's a significant percentage difference. All were about the same 7,800 GVWR. I typically travel faster than 60 MPH but slowing down from 70 MPH does improve the mileage. I don't find traveling with empty tanks improves MPG; it's really all about wind resistance. I have never had a high camper shell; always have had a flat fiberglass bed cover. I don't think the length will make much difference either.
