On my aresti's (2 of them) I cut a hole in the tray aft of where the original servo holes were. I mounted the rudder servo right in the middle and to the rear of the tray. I used a cut off giant scale horn and I have gobs of control throw. The only trick part is getting the screws in. I drilled 2 tiny (small screwdriver size) holes to allow me to screw it in..

You may want to give it a whirl. This is a great flying beginner pattern plane. Both of mine have only needed one to two clicks of trim and they fly straight as an arrow.

Matt