Position you servo and mark where you want the servo screws to be located at. Remove the servos and drill a 1/16" hole in each location. Use your servo mount screw and screw it into the hole you just drilled to cut the threads into the wood. Remove the screw and then wick some thin CA into the hole. This will harden the threads you cut so that they won't pull out. Make sure the CA is completely cured before you install you servo.

Hope this helps

Ken