For places that need a bit more strength use a medium t-pin (or a great planes wood pecker if you have one) to poke a lot of little holes in the area to be glued. This make little fingers where the glue can soak into that REALLY grab. This works wonders when gluing plywood, like the wing joiner.

I use my wood pecker perfusely (disrgaurd the phun!) for strengthening joins everywhere during construction. Really makes a difference in the final strength of the aircraft.