I used to believe that if one was one pound overweight, it could be considered negligence. However, appearance is important, as there isn't any real way to weigh things. If the truck/trailer combo looks too bad to a lawyer-appointed "expert" who will have access to the trailer's dry weight (and knows dry weight is a fictional figure), the negligence charge might stick.
It is understandable that it is hard to compromise on a vehicle that can tow a decent trailer, and is short enough to be able to navigate (as well as park) in urban areas. I've found that the best compromise would be a shortbed one ton with an extended (not crew) cab. It is a foot longer than a F-150, but not so long that there is no way to squeeze in a tight place at a mall. Plus, with this vehicle, you can use some truck campers, and with a slider hitch, can also tow most fifth wheels without issue.