Two primary limitations in terms of payload are the leaf springs and the rims/tires. The first can be overcome with SuperSprings and the second with the use of 19.5 rims and tires. Cost of SuperSprings is $500 and for 4 19.5 wheels figure on $3500.
Or you could get a lighter camper that weighs 2400 lbs. or less and get buy with E tires like the Nitto, Toyo,and BFG that are rated for 3750@80 PSI or more and will work with a 3400 lb. camper load (fully loaded).
A 4-season kit will add at most 100 lbs. as all that is done is double pane windows and a tiny bit of insulation.
Check out the Lance campers which are some of the lightest you will find and very well designed. A brochure with specs can be downloaded from their website. Good idea to get a camper that can hold two batteries and the optional solar panel is worth getting as well.
