Woodpeckering the coro and polyurethane glue gives the strongest coro to coro bond, IMO. If your tail feathers are just the thickness of the coro, you will have problems. On the pictired gasser, I ripped a yardstick in half and used that as a spar for the tail feathers. I then doubled over the coro, much like a wing is built. If you are too far along in the build, you could try to embed hard points in the tail and use tail braces, but I don't think I would ever trust single thickness coro on a bird that size.