There are 3 products that will help with Wander
The Safe-T-Steer (And their competitors) are one of them, I know my blue ox really helps.. Get the remote kit with the Safe-T-Steer
The other two are front and rear Trac Bars.. This is what the sales peson is talking about
Here is what happens with leaf spring solid axle suspension
The body of the coach can move slightly side to side over the axle. Now if the rear moves left and the front to the right..... You think you are drifting right and correect.. when they swap (And they will swap) you now think you are going left and compensate.
INdependent front suspension (On vheicles that have it) This can not happen but on a motor home you usually have a single I-Beam all the way across.
Likewise on a car with front wheel drive the way the rear is designed prevents it. but on a motor home (Rear wheel drive) it is like the front of the MH.
A Trac Bar very firmly LOCKS the body directly over the axle... Totally eliminating this "Wag" effect 100% eliminating it, One of the best improvements you can make.. I did, big time improvement.