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Pic 1 - remove the hex head (6mm) screws around the bottom line of the fender liner.
Pic 2 - remove the 10mm bolts at the trailing endge of the undertray.
NOTE - do not attempt to remove the SS nuts (2 on each side) that hold the bowden cable inside.
Pic 3 - Undertray removed, this is the proposed path of the duct.
Pic 4 - First hole cut (messed up one of the screw holes).
Pic 5 - Second hole cut - the mangled bowden cable courtesy of my hurried attempt at removing the undertray.
Pic 6 - View from the other side - notice how close it is to the hump profile of the undertray
Pic 7 - Passenger side flange cut and drilled, fits pretty good.
Pic 7 - Driver side flange, just flip the cutting template. (Don't worry about the cable, I replaced it).
Pic 8 - View from the inside of the tray.
Pic 9 - Finished flanges (polished/sanded, primed followed by rubberized paint).