Now for the questions about 5th wheel hitches and short beds....
Before you start, get your truck weighed (you, a full fuel tank and all its accessories). This will be known as your unladen weight, or curb weight. Then know your Gross Vehicle weight rating, Front and Rear axle weight ratings. These will probably be on the door pillar. Finally, look up the Combined Gross Vehicle weight rating (probably in the owner's manual). Subtract the UW from the GVWR and CGWR and you will be able to pull a trailer that will be less than these weights! It's less because you must account for passengers, cargo and the hitch hardware. The pin weight of the 5er is carried by the rear wheels and will be added to truck's weight.
Whatever you do, DO NOT trust the documented weight recommendations because every truck may be different by quite a few critical pounds and those numbers are only estimates anyway.
Right off the bat, a short bed will probably require a slider 5er hitch which weighs more than a standard 5er hitch, so this will allow less weight for the trailer itself. Some will NOT buy a slider thinking they'll not need it to save money and weight, but the dents of a truck cab are very expensive to fix (seen plenty of these problems) and then you'd end buying the slider anyway and spent more money that you planned to save.