What did you guys use for wing joiner tubes?
=========I got mine from Gator RC. $23.00 for the tube and phenolic insert that goes in the wings. It's really nothing to it.

How do you secure them together so they don't slide apart?
========There's a couple ways to do it. I just used a nylon strap, sort of like a landing gear strap, and strapped it across the split. I mounted ply blocks in each side and tapped them into it. since you don't see the underside of the wing, it doesn't really show. Only time I've ever had it apart was during an inspection. Here's a couple pic of the tube and joiner. The wooden dowels are obviously to keep the wing tip from twisting. I also inserted hollow tubes in the wing tips for the dowels to slide into, so vibration, etc. wouldn't wear out the holes. Probably just the ply facing on each root would have been enough, but to each his own I guess