RV Upgrades.com sells a product called the
Blue Ox Tru-Center. This may be a solution for you.
Before investing in additional equipment get your motorhome weighed so you can see where the weights are. Adjust your tire air pressures up somewaht by 5 to 10 pounds and try that and see if it'll help.
On the W-22 the best device that I have seen to reduce "yaw" exponentially was a rear mounted track-bar. A front mounted track bar improved the steering & handling and a Safe-T-Plus reduced the effect of bump steer.