I was thinking along the lines of having some vents to get the air in. It looks like you are using the factory vents in the rear quarters. Is that correct? I don’t have a really warm and fuzzy feeling about how much air those factory holes can flow.
What is the surface area of the existing holes? How big is the turbo?
Have you considered using some NACA ducts? They would work great in the quarter. But they would probably work in the under-pan too.
But you need to get the air back out of that rear area. On paper you want the ability to flow more air out then you are flowing in. It will keep the air a lot cooler in the compartment; it will significantly improve airflow in too.
I have an “exhaust vent” in the back of my 07’ located in the low pressure or vacuum behind the car. It draws air through the rear compartment really well. I’m using mine for a different reason (I have a heat exchanger back there) but it’s the same concept.
Something to consider.
