We did with our 1999 Coleman Utah and Jeep Laredo combo. The dealer gave me a choice between the screen room or accessories...I choose the sway bar. The following year, the dealer was selling the sway bar as part of the deal as a "required" option with the Utahs and Baysides.
CampingGeek
Cameron Park, CA
2003 Chevy 1500HD 2wd, 6.0L, 4.10 rear
Outback 29FBHS in tow (formerly Coleman Utah).
I only have a WDH on my E4, but with the length and dual axel, I have not had any problems with sway. I pulled it from VA to CA in May and never an issue. On a smaller single axel trailer, I could definately see the benefits.
JCH
New TV: 2008 Dodge Ram 3500, 6.7L Cummins, 6 Speed Auto, No mods yet (but they are coming)
2008 Fleetwood Evolution E-4, Reese Round Bar Weight Distributing Hitch
Me and the Wife: Scuba Dive, Mountain Bike, Kayak, Hike
Two Dogs: Mako and Amber
I installed a friction sway control on our pup (2007 Fleetwood Seapine). It towed pretty well before the sway control so I am not sure how much it improved the sway. I am sure that it did something. Watch out how tight you adjust the friction type controllers. I tightened ours slightly too much and it felt like I was driving a semi instead of a mini van (2007 Chrysler Town and Country). It made the van really lean into the curves...at least it seemed like it.