I had a Safe-T-Plus installed on my Itasca 30T. Helped a little but still lots of wander. Had a rear sway bar installed ($1,000). Mostly solved the wander to the point I don't feel the need to spend more.
Not knowledgeable on the Workhorse chassis but on an F53 at the age of your Mountain Aire the bushings in the rear sway bar are gone, if they haven't been replaced.
The other factor not mentioned in previous posts is the wheelbase length to overall length. Early 2000's Newmar's on F53 chassis had a poor wheelbase to length ratio and were subject to tail wagging the dog. Not really correctable. Reason I bought "some other brand" in 2000.