Carve, sand and shape your foam tips. Then apply layers of silk span with white glue, getting it as smooth as you can. Lightly sand between coats of glue/layers of silk span. Blend it in to your wing. You may be able to adhere the covering this way, or at least you can now paint the tips. Just let everything dry thoroughly. Another thought is to shape the tips, cut them loose, then lay up epoxy and fiberglass on the tips to get the shape, then dig out the foam from inside the glass. You can make cowlings this way also. The original "Lost Foam Method!"
Type at you later,
Dan McEntee