For my 90 sized plane, I use a 4-40 bolt threaded into the wing tube and the corresponding supporting plywood plate. This time I put the bolt on the upper side of the wing (so I don´t have to flip the plate to assemble it)
I tried a different approach in my Webra 1.60 powered Lazulite: one single alignment peg in the back, and a large plastic bolt secured to the root rib with a 5-ply wood plate between the peg and the wing tube. It is very easy to screw a ribbed plastic nut from the inside when you remove the canopy.