I wish dave, no that is what I get empty with my f150 supcab 4x4 5.4l. I did a 120 mile round trip from northern ohio to central ohio(flat land North to south). If I run around town, I get 16 MPG. I learned with my Rialtas, most the loss of Gas is getting the big beasts moving(truck and Rv).
I did average 17.5 through the appilacian mountains on my home from SC with my TC on my Truck after buying it there. I was down to three options, 1.) small truck camper, 2.) Aframe hardsided popup(aliner type), or 3.) Roadtrek type van. I crossed out the road trek as to get anything built in the last 10 years, I was looking at $25k and up. I crossed off the Aframe as it would add too much length to my setup, limit my offroad use, and wasn't as covert as a TC. Plus I scored my 2000 starcraft from a retired couple for $1400(with Roadmaster suspension, turnbuckles & Torklift tiedown complete setup). It is literally in mint condition inside and out and hardly used(hence why I drove from Ohio to SC). Getting in and out of my TC is a bit of a pain, but I will get some steps for it. I figured it was a no brainer way to test the waters of truck camping.