Back in '91 I purchased a heavy duty half ton Chevy with the intentions of buying a camper. In-laws had one we could use, so we decided to use it versus spending the money on our own. Bumper pull, over 30 ft in length and with the rear bedroom, it was very easy to get tail heavy. It had WD hitch, but with the rear bedroom (and all that space under the bed for storage) it was easy to lighten the load on the truck but impossible to do that and keep the trailer from swaying! One of the things I tried was adding coil springs above the leaf springs on the rear of the truck. That stiffened up the rear springs, but only when it was loaded, which worked out great. No air to worry about, or what happens when you blow a bag 1000 miles from the nearest shop that carries your bag! I called Chevy to make sure that adding these springs wouldn't void my warranty. Adding springs to level the truck was ok, as long as the weight didn't exceed rated capacity.
A friend was impressed with them on my truck, and wanted a set. We removed a set of coil springs from the rear of a mini-van, and adapted them to go on his Ford truck. It really isn't very hard to adapt, all you need is a mounting plate to hold them on the top of your springs, and U-bolts to hold that adapter plate. The top fits around the rubber bumper stop.
David from jax