Sway is the side to side rocking of the motor home,, Like fans at a music concert holding up their BIC's and swaying side to side.
SWAY bars are installed but on many motor homes an UPGRAD is .. Recommended
Wag is more like a dog's tail,, as the dog wags his tail side to side his feet (The tires) remain firmly straight, but the body may wag opposite the tail.
On a motor home, with leaf spring and solid axles, the body can move slightly side to side,, Usually the front moves one way while the back moves the other, then they swap, so you THINK you are going down the road like this /\/\/\/\
When in fact its like this -------
You tend to compensate, which makes your path more like the zig zag, and also makes it worse, and tires you out
TRACK BARS, also called Pan Hard bars, stop this dead, 100%, Eliminate it completly..
Finally steering stablizers, these devices do their best to keep you going straight,, Blue Ox Tru-center has a feature where you can re-center it from the driver's seat if its a bit off or if you have a strong and steady cross wind or a high domed road.
I believe it is Safe-T-Steer that has that as an option.. I recommend either the Blue Ox or the one with the option, with the option.
Hope this helps.