I put together the long spar for the vertical stabilizer and was fortunate enough to have read ahead to avoid some problems. The first one was that the M4 rivnuts did not fit in their holes, so those needed to be drilled out. No problem there. There are two layers of rivnuts, though, and if there are no clearance holes, the multiple layers of the spar don't lay flat. That was one of the tips I saw - make the clearance holes for the edges of the rivnuts. There is a picture showing the gap, then another one showing the layup without the gap because of the clearance holes.I also included some pictures of the clearance holes. Oh, but wait! The goal is to put M4 bolts (screws?) into the rivnuts eventually, which means that there needs to be clearance holes for the bolts to go through. Luckily, that was also a warning I read, because if I didn't predrill clearance for the M4, I couldn't do it after it was riveted together. The rivnut in the back would be in the way. There is a picture showing the other part of the spar with clearance holes for two rivnuts (in red) and the seven rivnuts (in green) on the innermost piece. There was also a "be careful" in that the brack that goes on the spar needs only 4, not 8, rivets. That would have been easy to miss. And, for the sake of completeness, here's what the "skeleton" looks like. Next step is figuring out how to put in the wiring for the strobe and the VOR antenna, and actually getting that done.