Deadband first.
This tells the computer where to start accepting input. If your getting huge swings with just a touch of rudder I'm willing to bet your deadband is the problem.
In setup/controls/joystick/settings wiggle the rudders so they just bump up against the springs. All you want to do is wiggle them in the center. If your seeing any inputs in the top blue box, increase deadband until you don't.
(This could be harder to test with rudders than a stick. With a joystick I either use pinky finger to "twirl" it around the center, or lightly move the base in a circle to accomplish the same thing. What you want is to find where the "edge" is that its picking up. Then set the deadband so its slightly higher)
Damping unless you have a spiking pot in the rudders can be safely left no more than a half inch or so up.
If after setting deadband the problem remains. Your going to have to tune it down with the sliders on the left.
Make sure your selected to rudder in the top scroll bar.
Set the first 5 sliders very low, not at the default 45 degree angle.
0 should be full down, then raise each one the thickness of the button on the slider. Or about 1/4 inch in my screen. Do this for 10 - 50.
Now you still want to end up with 90 at the very top. So set 60, 70, 80 to split the difference remaining.
End picture should look like a low curve, instead of a straight angled line.
Test them, see how they react now. Then go back & fine tune as needed.
Once your done, BACKUP your settings folder!
Save it to floppy, burn it to a CD, copy it to a second hard drive, or all of the above.
Trust me, will save you anguish down the road.
