OK, I know a few people have had this issue, others say not.

I have an 818S, and a dual exhaust, out the back. I do not have a spoiler or rear wing.

The exhaust smell in the car is OK for short trips, or highway speeds, but at low-med speed, I get a lot of fumes in the car.
I know Hindsight modified his exhaust to exit out the side, which cured the problem. I don't want to do that.
Has anyone else come up with other solutions before I start to evaluate options?

I plan to look into the following:
1 - clear lexan to completely fill in the rollbar area.
2 - some type of under bumper splitter deflector
3 - some type of bumper extension just above the exhaust exit
4 - addition of a rear wing or spoiler
5 - any other ideas??

I don't know much about airflow around the car, so any help from those who do is appreciated.

If someone has already posted this issue and I missed it, just point me in the right direction.