Yes right, sorry. Our truck is a 2006 Isuzu NRR flatbed with a max payload of around 11,000 pounds. We have been towing the sailboat (around 3200 pounds) for 11,000 miles without any real issues. We get about 9 to 11 mpg depending on wind and speed.
Actually I am not sure you can even tow a F150 or F250 with wheels on the ground. I just found the manual and it says they can't be towed if they have electronic on the fly shifting, which almost all of the ones on the dealer lot do have (you would have to special order one with manual locking hubs).
Here is a pic of our setup. I have a thread on here about the build too:
Flatbed camper build