Air dam / Air foil on cab roof or camper cab over?

Drag coefficient or not, any increase in airflow efficiency with my TC is always welcome, but then, I don't have the high frontal area that most of you do because I have a pop up so the roof is lower and the presented frontal area is less as well.... by about 18" actually.

I didn't excell at physics in high school.

One nice thing about my TC is, there is a number of convenient attachment points on the underside of the cabin over that are already there.