Safe-T-Plus and RSS are Stablizer/Dampers, in that they have Springs to press the steering toward Center, and hydraulic Damper (shock absorber) similar to what's already on your E350 Stripped Chassis. Steer Safe has only spring centering, but you can probably leave your OEM Damper in place. I"m not aware of other brands, not even of "re-boxing" on these three brands.
First, are you having a problem?
Have you weighed his Vegas, loaded as for a trip, and adjusted the tire pressure according to axle weights?
RSS is from Roadmaster. RSSA is for Class A anc RSSC for Class C (like E-Series) Safe-T-Plus isn't affiliated with Roadmaster. Roadmaster is a great brand line, but the S-T-P seems to have more followers and a better reputation.
S-T-P is the one installed by Henderson's out in Oregon, one of the top RV Ride and Handling shops on the planet. They say adding S-T-P is equivalent to setting the alignment CASTER angle to 5-degrees. Center of the Caster spec is 3-degrees but 5-degrees or a little more, helps RV's to track down the road. That's been well proven here.
I'd do these in order and evaluate
Weight and Tire Pressure
Alignment (need a shop who understands Ford Twin-I-Beam alignment with offset bushings)
Rear Sway Bar Upgrade (1-1/2" Hellwig)
Steering Damper/Stabilizer (S-T-P)
Front Sway Bar Upgrade (1-3/8" Hellwig)
Rear Track Bar (SuperSteer/Henderson, Blue Ox, Brazzel)
