Body sway and body roll are two entirely different things.
It's kind of amusing that the manufactures call them sway bars because they won't do a thing for sway. :h
Now body roll? Yes, they will really help.
If you want to take sway out then you need a panhard bar.
X2 on what Ben said. A bigger sway bar will affect handling. We play with bigger and smaller sway bars all the time in the racing game to get the car to come around or to push more.
But then again I hope nobody throws their camper into a corner at 90 MPH. :B