I usually like to epoxy (with a little glass cloth) small thin metal washers under the cowl where the screws will protrude. This reinforces the cowl sections where most the the stress is concentrated. These also allow you to tighten down a bit more on the cowl screws without cracking the cowl. Also, if the screws loosen, they won't wear through the fiberglass cowl thanks to the washers. I also use nylon washers on top against the cowl (rubber/lexan?... where do you get these?). Might be a bit of unnecessary work on small cowls but works wonders on larger ones. Some also install blind nuts to attach the cowling to the fuselage. CA-hardened holes (preferably in ply) usually suffice.