Pulled boats for many years, now have a Rockwood Minilite 2014s. Pulled by Ford F150 Lariat. Gas mileage went from 16 mpg to 8mpg. Just want to see if this is about the average drop in mpg. Don't see ...
Not always half, it depends on how slick the tow vehicle was before you hooked up a big box behind it.
My big boxy van gets 15-16 MPG at highway speeds not towing, drops to 9-10 MPG towing. A relative with the same drivetrain in a F-150 crew cab, slightly higher gearing, got 18-19 towing, dropped to 9-10 MPG towing. I suspect if you got a slicker, more modern pickup with six speed automatic capable of 20-22 on the highway, you would still be close to 9-10 MPG with the same trailer.