Wind resistance, not weight, is the big killer. If you want to get better fuel economy, get a rounded, low profile trailer like a Scamp, Casita, Oliver, etc. I have towed a little Burro molded fiberglass TT with my '08 Highlander V6 and averaged 14.3 mpg on a long trip. A similar trip towing a 2011 KZ Escape E14RB netted me 12.3 mpg. Both about 7' wide. The Escape was probably 400 lb heavier, but the big difference was the greater frontal area on the squarish TT versus the rounded, shorter Burro. I'd really feel it in a strong headwind.