From my experience with installing (and using) my Steer-Safe, it sure sounds like yours was not installed completely or correctly. As others have said, the eye bolts need to be very loose (nuts on just the first few threads) while the brackets are positioned toward the vehicle center. After the brackets are tightened, then the eye bolts should be tightened all the way down. This puts the correct amount of tension on the springs. Slight centering adjustments can be made from this point by loosening the correct spring(s).
Your expectations may be a little too high on the results you receive from the Steer Safe. It will never eliminate the need for frequent corrections unless you can teach it to adjust for road crowns, cross winds and rutted highways. It's just not going to happen, however, the improvement should be very noticeable.
The main purpose of the Steer Safe is to keep the wheel straight in the event of a blow out or a wheel drop off the pavement at driving speeds, but it does make driving and steering easier when installed properly.
Your own driving habits contribute a lot to the "constant correction" syndrome. You (any of us) need to focus your eyes about 150/200 yards down the road and steer to that spot rather than watching the road directly in front of the coach and constantly correcting to keep the vehicle exactly in the center of the lane. Let the old girl "wander" a little bit. Try it, you'll like it.