Actually from the sounds of it from VF that using the nylong bolts in the rear was a pretty good idea instead of the dowel. So maybe i did make a good decision. Granted from way it is designed i dont think a gap could form near the middle of the wing unless the epoxy gave way a little in the wing. Which i highly doubt.
Also it sounds like you reinforced the joiner as well. I smeared a good amount of epoxy all around the joiner near the root of each wing. Should keep it from splitting if there was micro cracks in the wood from mfg.