Again, Henderson's Line-Up - They're located close to Roadmaster and they sell lots of Roadmaster components. Yet, they endorse Safe-T-Steer not Roadmaster Reflex. Just looking at the two products, Safe-T-Steer uses two protected opposing springs to push the steering back to center. Reflex uses one spring in a Push-Pull manner for centering. I'm no engineer but it seems the two-spring arrangement would be more precise.
Your Safe-T-Plus would be the silver-gray "140" series. That means 140-pounds of centering pressure. Just remember:
1. You will also need S-T-P's appropriate bracket kit
2. You must adjust the S-T-P to make it center and not push the steering off to one side
Don't forget to weigh it and adjust those tire pressures.