I love a gooseneck but not for a short bed truck. For a short bed you need a slider and that means a regular hitch. There are pin extensions, and goose ball pivots etc. but to keep it simple, a gooseneck is best in a long bed.
You are failing to consider the CARGO/Carrying capacity of the truck as the main factor. Towing capacity does not matter with a 5er. With a Travel trailer most of the weight is carried by the axles not the hitch. With a 5er the hitch carries a lot of the weight. 15-20 % or around 2500-3600 lbs for a 18000lb loaded 5er. That is what matters with a 5th wheel tow truck.
What everyone is saying is get a dual wheel truck or smaller 5er. That is not to say you will not see someone pulling a 40ft monster with a single axle 3/4 ton, but it is not good for the truck to work at its limits all the time.
