Looking at the Goodyear inflation chart I would have to say that you divide the weight of that corner on the rear by 2. If not then you would have less load capacity from a dual setup than a single.
Part of the sway when going slow is from the anti-sway bars. They work great on the freeway or when corning. When going slow and hitting a bump with one tire the anti-sway bars will push the MH to the other side. The anti-sway bars try to keep both wheels the same distance from the chassis.
It's a toss up, heavier anti-sway bars or lighter ones. A MH has a high center of gravity so you need strong bars on the freeway or when cornering. The down side is more rocking when going slow and hitting a bump or pothole. It's never going to ride like a car. Workhorse did upgrade the front anti-sway after 2003, ours is a 2003 as well. They changed from a 2" square tube to 2.5", The rear should already have a 2.5" bar. They use to sell the bar and brackets as a kit. Now you have to buy the bar and brackets separately so of course it costs more. UltraRvProducts sells the parts if you're interested.
SoCalDesertRider wrote:
Heavy duty rear sway bar with polyurethane bushings will help with side to side rocking, as will upgrading the rubber bushings in the front sway bar to polyurethane.
I agree with BluegrassBill, the shocks are likely worn out and Bilstein and Koni both make good shocks.
I would run all the tires at 100 psi and see how it rides.
The W22 chassis has square anti-sway tubes bolted directly to the leaf springs, no bushings, not the more conventional round torsion bar. 100 psi all around will make it ride lock a rock, not a fun ride.
The bouncing does sound like it's time for new shocks.