AFAIK, pretty much all cars/trucks/buses have front anti-roll bars standard. Some have rear as well.
If you want to control roll, then yes, you want more roll resistance. This can be retrofitted with either thicker anti-roll bars, or additional anti-roll bars. IIUC, front anti-roll bars have a greater effect on total roll resistance than the rear ones. this is because most vehicles have front-wheel steering, so it is the front end that gets kicked sideways when you turn the wheel. It is this kicking sideways motion of the front wheels that causes the top to tip over in the opposite direction producing roll.
Does your coach / tow vehicle want to change direction when you are being passed, or does it tend to just roll over to one side without changing direction? If it changes direction, then that is often corrected with a panhard rod. (Assuming that you have a solid live rear axle, likely mounted on leaf springs.)
I am by no means an expert on suspension systems, and I will willingly accept correction on this. I am just trying to point out that there are different behaviors that can be addressed with different add on options. The term "anti sway" is too imprecise to define a particular device or a particular problem. I am just suggesting that you be aware of this when you talk to a true expert. Make sure that they know the difference, and that they will give you what you really need. Sadly, just like in any other business, there are those that know, and then there are those that only think they know. YOU need to have enough knowledge to tell the difference.
