My truck conversion weighs about 28k lbs. In May I took a 4800 mile trip from MN to CA and back. Kept my cruise speed 72-74 mph. Overall I got 9.8 mpg. Best tank was 11.3. Worst tank was 8.4.
Just another note. There's no real governing body but the term "toter" has come to mean a truck with smaller/medium size living quarters and a deck on the back for a fifth wheel hitch or goose neck. "Truck conversion" seems to refer to a truck with full length box for living quarters. Tben there are "garage coache's" that are a truck conversion with a garage in back.
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio