Every thing depends on which F150 you have. some can't tow or carry anything. Some can tow, or carry a lot. Some have a GVWR of 6500lb, Some have a GVWR of 7700lb. So the first thing you need to know is what truck you have.
Then focus on the weight of the trailer. You will run out of weight long before you run out of length. In fact, Neither Ford, or any other manufacturer mention length in their tow specs. Well Jeep use to. No longer I don't believe.
So find a trailer that is within your tow capacities when loaded. Remember. the higher the trucks GVWR the better, and the lower the truck rear gear the better.
