Servo grommets work in every material, and on any cowl. Cheap, available, easy to install without the need for glues, will not slip or allow the cowl to slide underneath as fuel tubing can (I used to use this method), reduces the contact of the rough back of a fiberglass cowl to the covering or paint around the fuselage, stays on the cowl when removed and reinstalled, can be painted to match the airframe, indeed, what is not to love.