In reviewing the plans before assembly, I noticed that the cabin area was a structure composed of many little uprights joining the top cabin longeron to the main fuselage. The plans call out some 1/8X3/16 doublers along the top and down the front and rear cabin uprights. The guru I consult with is Ed Hamler and he said that he ran 1/8 square spruce as doublers inside to “box in” the cabin. I also was concerned about the simple butt joint from the front cabin longeron to the main fuselage because that joint is where the wing holdown dowel is inserted and takes some stress in flight. I decided to run my spruce upright doubler full length

so it covered that joint (and hopefully, re-inforced it)That meant the cabin top longeron doubler would butt into the full length upright doubler at that corner. I used inexpensive spring clamps I bought at “Harbor Freight Tools.” The small spring clamps have good but not excessive tension and a level clamping surface. So it enables gentle application of pressure to the mating surfaces which assures a good bond. I also overlapped the long scarf joint at the rear cabin Longeron with the spruce doubler. This required matching the angle of that joint so the doubler didn’t poke out of the outline.