I've never reinforced before, but frankly, this GP RV-4 cowl is thinner than the other stuff I've done before... all Sig kits, I think. I'm considering it this time. Haven't decided yet.

You don't see it in my photos, but I did reinforce around the prop shaft opening by cutting a circle out of a flat piece of scrap and cementing it to the inside of the cowl, so now it is double thickness around the hole.

Phil