The strut on the bottom of the wing gets a doubler for strength (I presume) and this is made from a pre-fabricated strut angle and a gusset. The first task was to position the strut angle and back drill into it from inside the skin.
I did a lot of this from underneath the wing since it would be a real hassle to turn it over just for this small task. This made for some head scratching but was worth it in the end (I think).
To determine the position of the gusset I clamped it in place and made some pilot holes in a couple of the pre-drilled holes in the gusset and then removed it for drilling away from the wing.
After deburring and priming I riveted the gusset to the angle.
Then the assembly was riveted to the bottom skin, hopefully get some better pictures when the wing is closed up.