So what are folks average MPG when towing

Here is my numbers with my 1999 Dodge 4X4 24 valve Cummins. All stock, no chip. First I have a hard Tonneau cover on my 8ft bed, wash/wax truck, tires at full pressure. Normal mileage at 55mph with 410 gears in overdrive, 24mpg. One trip from SF bay area to Meridian Yacht plant in Washington state to pickup a Teak Deck kit for my 580 Meridian. Pulling my Pace enclosed car trailer empty to Washington I averaged 21mpg. Slightly loaded on return trip, (in the rain), 19mpg. Last week towing my 34' Stealth Toy Hauler to Corning Ca for the car show, 16.1 with 25mph headwinds. Towing back from Corning, (Rolling Hills Casino), 17.3 with very little wind. When driving I5 for example, I see guys towing 65-70 in left lane just blowing through their fuel. When I tow, I just relax in the right lane. Very little wear and tear if you drive easy. Don't settle for low fuel mileage. An open pickup bed with tailgate will slow you down a lot. Waxing your truck will help a lot as well. Tire pressures should be at max rated load capacity. The trailer should also be clean and waxed, tire pressures max for the weight. Oh, and the big thing for better mileage, leave the lead foot at home!