I've found CA to be the best. I think there is a flex CA on the market. Best bet is to throw away the plastic and get a glass cowling if you can. I know it's painful to throw away a brand new part, but plastic always cracks sooner or later. Usually sooner. I only got five flights before my last ABS part fell off. It was perfectly fit and mounted with large fender washers too. If nothing else, you'll save the hassle of painting a part that will quickly be replaced.

IMHO