The edge of the coroplast with the sheet rock corner support on the left, screwed to the framing strip on the right. Viewed from upside down.
Here is the undertray deflector that diverts flow back out of the exhaust tunnel, viewed upside down, see below.
The deflector goes around the exhaust pipe and is to keep air from going under the undertray via the exhaust tunnel. The main flow through the radiator will make it through the tunnel around the cat where it will hit the deflector about 1' past the cat. The deflector is held together by gorilla tape but that won't last too long. I will make a duplicate shield in sheet metal to replace it when this one fails.
There is a slight exhaust leak where my cat back exhaust attaches to the factree exhaust pipe. It is only a slip on U bolt connection. I need to fix the small leak as I can smell diesel exhaust fumes slightly now, when stopped at lights. Must be exhaust fumes trapped under the undertay. No smell when driving though.
So far I have seen a 13% bump in trip gas mileage with the installation of the undertray on my commute. Some of this bump is probably from the new front wheel bearings (one was bad), and some may be from the improvement of the undertray to the diffuser. The diffuser was installed first, which kind of traps air until the undertray is installed. I also have new rotors, the old ones were warped which may have caused some drag.
There is no doubt that I can coast farther with the undertray, and my terminal velocity of hills has increased where I need to use brakes now in a few places where I never needed to before. It accelerates much faster coasting on hills. Also after disconnecting my battery to do the heater core, when battery hooked back up, my idle fuel usage went from 0.16 gph to 0.12 gph, so 33% less fuel used now when coasting. I must of cleared some code. It got rid of an excessive vibration at idle.