I do not use a jig of any sort.

My method is this. The wing is finished with the centre section glassed. I have 3/4 dowels right through the wing at the screw locations (under the glass). I align and GLUE the wing in place with four small blobs of epoxy at the screw locations. By eye I drill one hole through the wing with the clearance drill. Again by eye I drill the tapping size through the fuselage mounting. I tap this hole and put a screw in it. I check that the wing has not moved, being glued it is not likely. I then do the other holes the same way. Drilling the mounting holes removes most of the glue so the wing pops loose easily.

Ed S