Aeromotions wing install
 

The wing is basically a portal frame. The thin aluminum trunk has zero moment carrying capability. Reinforcing the bottom, like Bob did, will spread the moment over a larger area. If you don’t like that look, you can probably get away with putting that plate on the inside of the trunk instead of the outside. You could stop the swaying by x-bracing it too. I’m assuming that’s what your shop was talking about doing with the cable. I don’t know what vortex vibration you might pick up on a cable or any x-brace you might use that is cylindrical.