You are going to hear that most people who tow or have a motor home or MH and tow are going to be in the range of 7 to 10 MPG. With our 30 ft. Class C with a V-10 towing a 2700 lb. car we get 7 to 11 but mostly around 9. Some will report better but honestly 2 or 3 MPG one way or the other doesn't make much difference within the context of the total cost of RVing. The biggest cost is going to be your truck and trailer; that is, depreciation. The best way to improve MPG in any vehicle is to drive as slow as you can tolerate. Next best is to loose weight.