If there is not enough room to use a servo tray or you want to try another method, this works well.
Basically all you do is wrap masking tape around the servo sides and base, then epoxy it down. Being that these are "life supporting" components there are some things to watch out for. First you want to use high grade masking tape 3M or Scotch. Make sure it sticks well to the servo and is a new roll. You may want to lightly sand the servo to make sure the tape stick well to it. You also want to lightly sand the tape after its been wrapped around the servo to make sure the epoxy sticks to the tape.
When you glue the servo down get as many side of the servo to touch the frame as possible, the more surface area that has glue the stronger the hold. To make sure the servo won't come undone blocks can be added to the sides not touching anything and glued to the plane and servo.
Once the epoxy has set pull on the servo, it should not move and should be very secure. This method works well and saves time but should be used on smaller planes (under .50) If you look in the photo section of the page the Little white plane near the top and the modified dazzler both have their servos mounted this way as does the U2 at the bottom of the photo page.