Looks great!!!
Just having that cooler is going to be enough. Ducting isn't really going to be an issue. Just install and go. If it's still too hot (
) seal the cooler to the trunk floor. If it's still too hot (
) create a front inlet and duct it to the cooler.
Trekkor and I did some testing awhile back and found that with any sort of front valence, airflow through the holes in the front is very small. They're good for getting a little fresh air. But not good as ram air unless you mimic Trekkors air holes.