Hi Paul, I just had a thought, is the rudder mass balanced?
If it isn't then try getting enough weight into the leading edge of the tab till it is actually nose heavy. If you lay the fuselage on it's side the front of the rudder should be heavier and it will go down.
This will naturally dampen out the the snaking, it may not cure it but it's an easy fix to try.
If the rudder is tail heavy then as the body snakes to the left the weight of the rudder tries to carry on making the effect worse but if it is nose heavy it will do the opposite which could cancel out the snaking effect.
Mail me if that isn't 100% clear, lol
It's confusing to me and I wrote it, ha ha
If you do add a lot of weight don't forget to check the cg of the entire model just in case you have moved it back.
Not sure if the cg of the overall airframe would affect the snaking, the model should very slightly drop the nose when flown inverted but only a little bit.
A customer of mine a long time ago had a large Mig 29, this had an elevator snaking effect. He found out it was because he had mounted the servos on the fibreglass body skin and they could flex. You could bend the skin by moving the stab.
Some twin finned model jets like the F15 can have snaking and can benefit by putting the rudders outwards a little bit which gives them "toe in".
I can't explain why this is but it seems to work.
Some aircraft have a plate fixed on the rudder trailing edge. Someone mentioned this earlier in the thread but that is an easy experiment to try although I think it is to stop rudder flutter or rudder buzzing rather than snaking.
Jim