I did not document what I done, just took a couple of pictures on my phone.
Just flanged, used cleco's like you did, after it was fitted to the car.
Pulled the panel off, cleaned to bare metal, applied a bead of 3M panel adhesive, shoved the cleco's back in.
After it sit overnight, welded the pinch welds.
Its holding up fine, I have no worries of it falling off.