Kitchen Cutting boards can work very well (not the wooden one's)_they come in all kinds of thicknesses and different colors (I stick with white) they are bacterial and mildew resistant, and once you find the right thickness you can use a jig saw to cut out the exact shape and profile that you need_you can even leave a longer section at the top so they will "hang" in place (self supported) making it easier to put them in or out.
