I agree with Manks. I have a PT-40 and it does not need flaps. What you can do is to use two aileron servos and use flaperons and increase their surface.

I have always considering build another wing with reduced dihedral to one inch. This is one side of the wing flat (0-degrees) and measuring the height of the other wing tip to the flat surface. I think the "B" dihedral is close or more than 2-inches. Also, you might want to modify the wing ribs and convert them to semi-symetrical instead of flat bottom. And finally, with the semi-symetric wings, reduce the incidence of the wing to cero degrees or +1.