Sedan-to-Kammback-Converter is now finished and on the car. I'm not expecting much aero gain out of this by itself though, thinking the clear-plastic gap-filler piece is critical for the gains, based on earlier tufting with the cardboard pieces, though the gap-filler should be a samewhat easier piece to make...
Let's see, what do I have left to explain about construction here? You can see the 1/32" textured neoprene rubber boots (couldn't find EPDM in that thickness) over the high-pull Nd magnets - not as aero as I'd hoped to make them, but doubt it matters much, or else maybe I'll do something about it later on... Also, the gasket closing the gap to the roof here is ferrite-magnet-doped rubber. It's not so good for holding an aero-mod in place, but it does a great job of closing a gap... although at $4 per sqft it needs to be used somewhat judiciously. On paper, it should be good for about 2 PSI holding power at 1/16" thickness. It feels 'about right' to me, and what you see here has been freeway tested a bit.
Mostly I'm using the "3X" Loctite construction adhesive on all the joints, the upper window is the exception with exterior caulk - thinking that piece might need to be replaced or upgraded someday. (Also I used #4 screws there instead of rivets, for the same reason.) The reason for the concern is that the view is at such an oblique angle to the window, little imperfections matter more than usual.
The c-pillar seals are 1/2" width foam rubber bulb.
I probably will need to tweak a couple of the seals to get them to behave when the trunk opens and closes. I.e. one of the magnet seals gets caught on the high-pull anchor, and a little section of the foam rubber bulb section gets folded over the wrong way. It's not hard to just walk around it and reseat the seals, but it would be nice if they just went back into place.