Drilled & clecoed rear-channel between ribs # 1 & 2. Bent flange on root channel to 30 mm. Cleaned, deburred & primed (t=0.40 shim) in front of flaperon supports that rear channel sits on. Much time spent trying to figure out the drawings, edge-distances & measurements for the channel & parts getting attached between ribs # 3 & 4, also, root rib. Having much difficulty figuring out rear channels & attaching parts.