don't forget driver and passenger(s) count as payload in the truck.
I'm seeing the Tab 400 has a GAWR: 3,500 Lbs, and max hitch weight
of 460 lbs, so way I figure, thats 3940 lbs GWR... between bedding, clothes, towels, food, beverages, its real easy to come out a lot heavier than you might think.
I'd skip any WDH type system until you've towed it a couple times and see how it rides. if the front of the truck is 'pitchy' when you go over bumps, then you might want a WDH. or if the rear of the truck sags too much when you drop the hitch weight
btw, T@B's are not considered molded fiberglass, they are framed and skinned like a conventional 'stick built'.