Problem with some ARFs (not just GP's) is that they leave a gap between the wing and mounting bolt plate. If the modeler cranks too hard on the wing bolts, over time the mounting plate will tend to bend or pull away from the fuselage sides - ultimately causing a separation failure.

Some ARFs have the gap filled in with balsa, which eliminates this problem. Personally, I do the same thing to ARFs that don't have this from the factory. It also has the added benefit of helping to guide the wing bolts down to the blind nuts.