Luke,

I mounted my rod and ball (with round aluminum ground plane) in the right wheel well on the inside wing skin just outboard of the tire.  This is that funny shaped area of wing skin outboard of that extra partial rib.  The ground plane bolts to three glass flanges that raise everything so that the ball is just inside the outer glass layers of the wing skin.  The inner layers of skin are cut away so that the radiating element is as close to outside as possible.  This way, when the gear is up, there is no nearby metal lower than the ball.

Have never had a bad report from ATC.

Tom Thibault