Wrap the servo with common vinyl electrical tape. (makes repositioning easier)

Buy 3M outdoor rated double-stick foam tape. Its grey, and sticks twice as well as the white stuff. Its also slightly thinner and has less flex... so the servo case moves less under load. (more positive control movement.)

You can tape the inside of the plane with clear packing tape where the servo will go, and that will act as a release layerso you can remove the double-stick foam tape without ripping the foam. (same purpose as the vinyl tape on the servo, so just do one, or the other.)