I don't think the weight is really going to matter that much. I mean you are adding the servos anyway, and you are going to use a 480 motor. If you can position the servos near as possible to the thickest portion of the wing, then all you are really doing is carrying a few more grams of dead weight. Not to mention making the installation easier, with fewer parts to fail, etc, etc.
In the end it is up to you, but this is a trainer, has a relatively large wing area with very light wing loading (based on the specs I looked at), so placing the servos in the wing just makes sense to me...