This fairing is my design. Oil flow photos on my flying plane suggest this wing/winglet intersection is good but at the trailing edge the high pressure air from under the wing separates the flow on the rudder up about a foot. So I'm just putting in a simple fence to prevent this separation.
I'd previously made some 3 ply BID for this fairing and cut it slightly oversized but to shape. Using the hot glue and some sticks I secured the fairing in place from the bottom as you see in pic two. I have set it in line with the airflow and about 0.3" below the rudder cutout so I can get a nice transition.
I lined the join with flox and layed up 1.5" wide tapes with the foil method on the top side. These will add a little extra strength to the fairing which I am mindful of needing some thickness in that position for ground handling and when cleaning the winglet. I've peel plyed the joins and will do the underside after cure...and a bit of a clean up.