I use 5000# helper bags on my truck(2500hd). I also Removed the Overload spring so when it's empty it rides better.
On-board air compressor and the use of a air pressure regulator the bags stay at a consistent number.
I've hauled a 40,000# gooseneck with it and 150psi in the bags, it handled it great.
I've never had the time to do the overland deal but have you thought about a SUV? I hog hunted out of a 2003 tahoe and had it setup where I could store supplies in a lockbox in the back and fold the seats down to sleep 2. Had made winch bumpers front and rear, 32gal aux fuel cell where spare tire was, spare battery under rear for rear winch and accessories, 4'x6' roof rack for spare and 800' of winch ropes/snatch blocks/recovery gear.