How did you end up doing the elevons? We had to do a differential thing so they worked on the appropriate side, ie: upper wing had only up elevator, bottom wing had only down elevator. And did you find the roll rate obscenely high?
No, the elevons are coupled together with a vertical push rod configuration or bottom control horn to top control horn, no differential. The roll rate is nice and comfortable. Some flyer will disagree with this, what you have here is nose heavy controllable flying dart with wings providing lift. In saying that, the CG is forward of the wings (1/4" approx.) then you have to set in elevon reflex (up trim) to achieve smooth level flight. When a balance between these is made you will have a very stable aircraft. When landing all you have to do is cut the throttle, keep the nose from rising and it will fly itself to the runway. Mine is still flying. I hope this helps have fun.