This next part is probably up there in the running for my least favorite thing to do.

Hopefully you still have the scrap laying around from where you cut your wing tips. If you look carefully, you'll find that this curve almost fits around the fin at the fuse. Well, sandpapr and a curved sanding block are about to become your friends.

There's no easy way to explain this. Just do it. Make these blocks fit as snugly against the fin and fuse as you can. You'll have to blend and fill this area, and wood weighs much less than any filler. So, get as much wood in place as you can without too much glue.

Add the dorsal piece. On mine I increased the size slightly, and the effects were wonderful.

Now after everything dries, sand, sand, sand