So I have the turbo and the car has a single exhaust on the right hand side of the car, however, on the left hand side is a open space where the twin exhaust would go on the cars with that option. On my car that area is open and leads to a parachute rear bumper. In this shot you're looking up at the rear bumper (top of image) and you can see the gaping hole that leads to a small section of parachute bumper:
Initially I stuck a piece of corplast, angled to meet the bottom of the car and to close the opening in the leading edge of the bumper. So here we're looking rewards, the bumper is now at the bottom of the image. Ran in this configuration for a couple of weeks:
But that was always just an interim idea. The angle of the panel was relatively abrupt and probably not ideal (not BAD, just not necessarily ideal, I extended the panel as far forward as I reasonably could). But I envisioned a infill panel with a rounded leading edge to slid into the slot, so I ended up shaping one out of foam sheet insulation (the blue kind you can buy at Lowes for $14 for a 4' x 8' sheet) and then laying up (in this case) carbon fiber over it. When everything was cured I ate out the foam insulation with acetone, not a particularly green process I'll admit to that, giving me a hollow box with the requisite shape:
I noticed on the exhaust side the bumper is open there too so I filled that in with the same angled panel concept I used on the opposite side (there's not room to really put anything in more extensive, plus I'm sure the airflow there is such that this one isn't doing much), just reversed.