Originally Posted by Adaycj
Frontal area may be a concern in this specific application.
Frontal area of the trailer is definitely a limiter. Frontal area translates into aerodynamic drag (wind drag). At highway speeds, the wind drag can be more of a limiter than trailer weight or length.
For a while I towed a 7x14 cargo trailer with a 2003 F-150 SuperCrew with 4.6L 2V engine with 3.55 rear end. The tow rating for that pickup was 6,200 pounds, but it struggled with an empty cargo trailer that grossed less than 3,000 pounds. Even empty, because of aero drag that trailer was too much for that underpowered pickup. After a trip from west Texas to Phoenix with a load of furniture in that cargo trailer, and the return trip back unloaded, I decided to trade that pickup for something with more towing power. You don't even notice the grades on I-10 in southeast Arizona in a tow vehicle with adequate towing power, but with that pickup and even an empty cargo trailer you'll definitely notice climbing out of dry gulch valleys and climbing over ridges.