RE: *Using Rubber O-Rings On Cowling*
What I do on all my 25% and larger planes is to use #10 nylon screws/bolts. I tap the wooden blocks, harden with CA, retap and voila! The holes in the composite never enlarge and the cowl never loosens. IMHO using metal screws/bolts and blind nuts - is nuts. I use nylon screws/bolts to hold the canopy frame as well. Never lost a bolt this way. I have done this ever since I lost a canopy frame off a 42% Giles during a snap roll. The flight & landing was a real adrenaline pumper!
Safe Flying!