I agree with Harvard.
That said, we had a 1971 Doge B300 Window Van. I spell that out because it was NOT dual wheel or RV chassis. But the way the front end was laid out, it had two Idler Arms. Those were critical to tightness of steering. Also, I replaced Control Arm Bushings along with Ball Joints. That too made a difference.
Re: S-T-P vs. Roadmaster (REFLEX I believe is what you are asking about). Two things favor S-T-P:
1. It uses TWO springs in opposition to help find "center." Reflex uses one. Off center in one direction, that spring does its job in Compression. Off center the other direction, same spring is working in Tension. The S-T-P design makes more sense to me.
2. An outfit in Oregon called Henderson's Line-Up is famous for its work in RV Ride and Handling issues. They have very close ties to Roadmaster but their steering stabilizer solution is S-T-P. That endorsement speaks volumes to me.
We do have an OP here who had a spring break inside the shielding of an S-T-P. The power steering force required to overcome the resulting jam damaged part of the frame. That's Bryan and he uses his rig HARD. Only documented case of a problem with an S-T-P here at RV.net.
My take: Be sure the ENTIRE Suspension/Steering are OK and that it's in proper alignment. Add a little Caster if you can, more than mid-spec range, but not more than max spec range, and see what it does. THEN consider an add-on. Your front end is more like the Stable Chevys than the Wandering Fords. Getting it all tight might be enough.