Yup, my E-Boost F-150 with no trailer gets 19 to 20 mpg at 70 mph on the flat with speed control.
Pulling a large Palomino Pop-up, my mileage drops to 14 to 15 mpg at 65 mph on the flat with tow haul on.
Pulling a 26’ Dutchmen my mileage is 9 to 10 mpg at 60 to 65 mph on the flat with tow haul. Add wind or hills and mileage drops.
That is life with a TT; weight, length, and shape have little or no overall effect on gas mileage, unless you can collapse it. Trailmanors and Hi-Los prove that but you can buy a lot of gas for the price difference.
Basically 10 mpg is the price you pay for pulling your house down the road.