I've replaced the stock sway bars on my E450 with aftermarket heavier bars. A worthwhile upgrade, helps minimize rocking. These rigs handle better if they're not flopping around down the highway. Heavier shocks do to, I have the Koni FSD. Suspension upgrades highly recommended.
The only slight downside I've experienced with the bars is the sounds from the polyurethane bushings. To me not annoying and can't be heard in the RV with windows up. But there is a light bit of suspension noise when windows are open and speed is slow. Probably heavy greasing and frequent maintenance would take care of it, but it isn't bad and I don't have a problem with it. Positives far outweigh this minor negative.