I use round servo grommets. Drill out the hole with a 5/32 bit, squeeze the grommet in. It stays in place in the center of the cowl, and also stands off the cowl from the covering or paint to reduce abrasion. A small washer can be used under the screw to compress the grommet. Here is an example. Most of us will have these grommets laying around.

PS. I wish I could do diagrams like Minnflyer.