If an installation would be conducive for using a servo tray, I would use one. However, many designs now install the rudder and elevator servos in the tail and aileron servos in the wing, so there is only the throttle servo to mount forward. We are left with few times that trays are useful, anymore. With the use of the metal eylet and large rubber grommets, mounting in a tray, or alone to hardwood or plywood is the same and fine.