I have little to no rear sway with my 2005 38R on a W24 chassis although I have more weight on the rear and less on the front than your 3 slide 38J.
There are a few things you can do before spending $$$.
Make certain you carry your feathers in the front basement compartments and your anvils toward the rear.
Weigh all four corners and adjust your tire pressure accordingly.
If I still experienced sway after exhausting a weight and balance I'd install a rear sway bar mounted from the axle housing to the frame rails such as Workhorse's bar pictured below.
__________________
Sarver, PA/Crystal River, FL/Hawthorn, PA · FMCA 335149 · W3TLN
2005 Suncruiser 38R · W24, no chassis mods needed · 2012 Honda Accord SE · 2008 Honda Odyssey EX-L