Dufault.. on the elevator joined by the wire... I always put a piece of fiberglass around that joint on each half. You don't have to but that area takes a lot of stress and it's just somehting i do. Over time that balsa will weaken.

I hope the pic makes sense. Basically a C over each half. I run it to where the wire stops in each elevator. My 4* 40 had the same setup with the wire joiner and never had a failure.