Another idea you might look at is clear plastic tubing. I buy it for .22-.25 cents a foot .. Most any hardware store carries it. It comes in thick or thin wall(what I use) in the 3/8 I.D. size. It will harden with the heat and may fall off once in a while but I usually secure mine so that it stays on. I keep a length in my accessory box I take to the field. If it falls off the plane it's no big deal. If the factory made deflector falls off you have lost $3.
Fred