We are beginning to look at travel trailers. One consideration is the cost of towing the unit. With the Middle East situation and with the government saying that our highways are seriously underfund...
I pull a 28ft TT with a big square front with a 2000 F250 7.3L diesel.
I avg 18mpg unloaded and 11mpg towing. That said, I've gotten as low as 8, and as high as 13 towing. A lot depends on how you drive.
In a hurry, gas mileage will suffer. I also get better mileage if I turn OFF the cruise control. Between 55-65 mileage is good. Go over 65 and it goes down.