The AF 811 is designed for a short bed but comes in two configurations so it will fit on short or long. If you get the "S" model, it will be exclusive for short bed because storage compartments are added to the overhang. The standard 811 fits long or short beds and has an empty skirt so it can slide forward more on long beds.
His trailer is much smaller than mine so tongue weight will not be such an issue. I expect he will be too close to the limits of a 3500 lb rear tire and should look for 3750 lb ratings or better if he does not change trailers.