The instructions said to lay the rudder on two boards and raise the lower trailing edge 3/4" to keep it even and prevent warping while attaching the skins. The ribs lined up pretty close to the pre-drilled holes in the skins, but not perfectly. The 3rd rib from the bottom was the farthest off. I had to bend this rib slightly at its attachment point so the proper edge distance would be maintained when riveting the skin to it. The top skin was a little too long and needed about 3mm trimmed off the upper edge. The instructions say this is normal though.
