A trip strip is a small strip of something added to the car body in an area where there is too much curvature to maintain attached flow.
Here is a strip added on the roof of a car. I'm guessing it is a bit to low to 'snag' the air past the boundary layer. A tuft test would reveal how effective it would be.
To get a good idea of what the airflow around your car is doing, it would be very helpful to do a tuft test on your car.
AutoSpeed - Aero Testing - Part 1
Once you see where the problem areas are, you can begin to address them.