The aileron-horns DO NOT use the backplate that comes with them-- use wood screws to attach the horn to the aileron. I remember thinking the same thing when I built the plane so maybe the instructions are not clear.

As stated above, I built the plane as specified in the manual... that means no glassing the center section of the wing. I have to assume that the manufacturer knows better on this matter (and I trust Great Planes), plus it just adds weight. I didn't go crazy in the 3 or so flights I have had but I didn't notice any sign of the wing being weak.