There’s no such thing as a single rear wheel ‘99 Dodge 3500.
If it has a manual transmission, it has a Dana 80 rear axle rated at 11,000 pounds, so if it’s a single rear wheel (2500) it’s limited mostly by the tires. If it’s a dually (3500) stock size tires will handle 10,800 pounds on the rear. That’s plenty.
If it’s a single rear wheel 2500 with an automatic trans, it has a Dana 70. Those have enough capacity for single rear wheels, but if it has a lot of miles on it, beware the Dana 70 is known to fail and need rebuilding a lot sooner than the 80.
The single most important thing about a ‘99 Dodge with a Cummins diesel is what engine block casting number it has. Specifically, whether it’s a “53 block”.
If it is, DON’T buy it unless you’re ok with replacing the motor. 53 block Cummins have a very common nasty habit of cracking and they aren’t repairable.
They were cast too thin and crack at the right rear.
Look under the truck at the engine block. On the driver side, toward the front, down low. If there’s a “53” cast into it in inch high numbers, run away.
If it says 54, 55, or 56 it’s fine. If it has a long series of 1/4 inch high numbers and letters, it’s the least common and most desirable Mexican block. (The 50-series blocks were cast in Brazil.)
Seriously, read up on how to identify a 53 block Cummins and DON’T buy one. I’ve had two of them crack in my own truck.
If it’s an automatic, it really needs some expensive upgrades. Plan on a $4000–$5000 performance-built transmission. Trust me, it needs it. If it was a 5th wheel hauler it may already have that done, but it’s hard to verify unless it has paperwork.
The Diesel engine (I’m assuming it has that) does not lower the payload as so many people and even the factories tell you. All the camper weight goes on the rear. A lighter engine (gas) up front does not help carry a heavier load, you can’t get the weight of the camper up front anyway.
There’s a lot more to pickup trucks than the length of the bed.
How big a camper you want to haul changes a lot about what truck you need for it.
2017 Northern Lite 10-2 EX CD SE
99 Ram 4x4 Dually Cummins
A whole lot more fuel, a whole lot more boost.
4.10 gears, Gear Vendors overdrive, exhaust brake
Built auto, triple disc, billet shafts.
Kelderman Air Ride, Helwig sway bar.