when you are moving a constant speed on a freeway, the air resistance is your biggest factor in MPG, not the weight. I have not towed a TT, but I did have a 6'-6" tall enclosed toy trailer. My truck would barely notice it driving around town, but once you get over 60 mph it felt like I was pulling a 12 bottom plow. And that one oven had the slightly V shaped front. If I was ever going to buy a TT, I would make damn sure the front of it was curved to be as aerodynamic as possible. A brick is not aerodynamic, and pulling one is the easiest way to kill your MPG even when empty.