Short beds have clearance issues when turning (normally while backing) a 5th wheel, so a sliding hitch is usually needed to keep the 5th wheel from contacting the corner of the cab of the truck. The 5th wheel hitch is normally mounted right over the rear axle. The extra 18" of an 8 ft bed (compared to a short box bed) puts an extra 9" between the nose of the 5th wheel and the back corners of the tow vehicle cab. The slider hitches give a short box some of that distance back to relieve the clearance issues. The extra wheelbase offered by a long box truck also adds stability in the towing environment when a big truck passes and the "bow wave" of air hits the trailer you are towing ... believe me, you can feel it, and the increased wheelbase is your friend. That said, a short box can work as long as you are careful with the clearance between truck cab and 5th wheel and you can live with the increased movement you'll experience with the "bow wave" effect.

Thanks for the info.

A crewcab dually longbed provides the most comfortable ride and a more stable ride when towing a 5th wheel.

Many highways are built in sections. A shorter truck will oscillate (buck) depending on how these sections were built and distance between the joints. This bucking occurs less frequently with a longer truck.

Occasional drawback to a longer truck- tougher to maneuver in tight curvy interior campground roads and campsites.

I prefer a dually longbed crewcab for the flexibilty (Passengers are comfortable, more space to carry stuff in the bed, heavier loads)