The sidewinder is your best choice, it moves the pivot back about 20 inches and you can use a lightweight 15K or 16K fifth wheel hitch (under 150 lbs). Auto sliding hitches are heavier and may not slide back far enough to work with under 6 ft bed lengths. The sidewinder has two other benefits, it makes the fifth wheel track more like a TT, so it will not cut inside the truck track as much when taking corners. Also, when backing up, the trailer will react faster to steering changes (which can be dangerous if not paying attention) so you need less space for maneuvering.
Make sure your truck has LT tires and you are not exceeding the truck's rear GAWR.
