I agree that hardening the threads with thin CA will make the holes last a long time.

Here's something else you can do if you're not happy with that solution.

Take the yellow inner portion of a nyrod pushrod.

Drill out the hole so the nyrod fits snugly inside. Scuff the nyrod and expoxy it into the screw hole.

Install the cowl with self tappping screws and (here's the secret for getting screws to stay put on gassers) use rubber bonded or sealing washers on the screws. RTL Fasteners sells the bonded washers in various sizes.