You mention stringers, so it must be aluminium.
Not being a tinbasher I would hazard a guess and say that you could have a doubler on the outside preferably to the next rib and stringer each side and a filler on the inside of a phenolic material like bakelite that is shaped to the skin contours and flat on the inside to absorb the load path. Another doubler inside would probably not be amiss if it is a fast-ish fixed wing bearing in mind the forces involved.
You could then bolt it from inside into the body of the fitting or through the skin from outside by means of a flange.
Anyone else care to shoot me down in flames? (and contribute their expertise)
