One word Silicone!

Plane old 100% silicone from walmart etc. Make sure you have all your holes lined up the way you want it, add silicone behind the screw location and around certain areas of the primiter for even more support.

What this dose it prevents the whole cowl from comeing lose working around the screw locations that cause the damge at those spots.

Me and my boys use it all the time on our Bigg 100CC + planes. Its great, and when you have to take off the cowl, once you remove your screws just slowly pully off the cowl. You will have to remove most of the old silicon before reapling as silicon will not stick well to its self.

It dose take all night to dry and its very easy to clean up if it squishes out past the cowl before it drys.

Good Luck Mike