Would Krylon 1311 Matt Spray help to protect my duck decoy's paint?

YES, I have used it on hundreds of duck and goose decoys for over 20 years. It not only protects new paint, but it also renews the oxidized color on old decoys. It lasts for up to 5 years with normal use, and 1 can will treat about a dozen magnum duck decoys. Reapply when dullness starts to reappear.