Considering my concerns about payload and the constraints of a short bed, can anyone tell me what the best lightweight options are for slider hitches?
Your getting the my brand is the best hitch regardless of your question for the lightest which the B&W isn't nor is it the best. The top auto sliding hitch on the markets and has been for years is the SuperGlide but it is heavy.
Many newer gen 5th wheel trailers have the notched/rounder front corners made for short bed trucks. No need for a sliding hitch.
A far as actual hitch assy weight you will have to go to each hitch makers and see what their numbers are. Hitch weight should include all rails or all the parts from the hitch down to the kit/brackets that attaches it to the trucks frame rails.
There are two lightweight 5th wheel hitches Andersen and the PullRite SLR series. Both use the same GN ball technology
Pullrite says their steel only hitch weighs 64 lbs.
Andersen has a aluminum hitch that they have said it weighs in the 40 lb range or a steel hitch that weighs in the 60 lb range.
And you will have to decide if you want/need a single point or 4 point attachment.
Check out each hitch mfg website how their system works.
The 3500 SRW Ram has a 7000 rawr that is going to carry all the weight in the bed. The Mega is heavy on the rear axle and may weigh in the 3400-3500 lb range leaving the truck with around 3500 lb range for a in the bed payload. Like all truckers you have the truck so get your trucks separate front and rear axle weights that way you will know how much real world payload the truck has.