Another reason I would always use foam tape glued to the servo and the airframe on these types of airplanes(this tape was marketed in the Jurrasic era of radio control aircraft as 'Servo Tape') rather than glueing directly to the airframe is to facultate easy removeal.

This tape is perhaps an eighth inch thick and it provides for easy removal simply by sliding a #11 blade between the airframe and the servo thru the foam. Far easier to do and easier on the airframe.

John