I've started my Edge540 build finally after documenting all the info I could gather from VF and here. They have been great about sending me extra assembly photos of the first steps . I have the wing joiner built and cured out. Mine fit into the wing root slots with very little effort. I'm still going to lightly sand the joiner before fitting to the wing so the epoxy will have a bit more room to spread.
A friend suggested Gorilla Glue as a substitute for the epoxy. It soaks into foam deeper ,,, unlike epoxy that only adheres to the surface of the foam. But I think VF feels that their instructions will work just fine. They really have been quick to reply to all my questions and make you feel like part of the family when you purchase one of their ARFs.
I too may have a modification idea on the back wing guide that would secure the TE area firmly to the fuse sides. More to come.