Will this diffuser scrape on driveways or steep inclines?

The DTM profile adds extension to the lower rear. Test your approach and departure angles in your driveway before final installation. If clearance is tight, adjust your suspension ride height accordingly or verify ground clearance at parking lot entrances you frequent.

Is this diffuser functional for downforce, or is it purely cosmetic?

DTM design elements are styled for appearance and visual aggression. Real downforce requires aerodynamic testing and integration with your entire rear end setup. This diffuser complements that look but should not be expected to generate measurable downforce on its own.

What prep and finish should I apply before installation?

Sand and prep the FRP surface per your chosen paint system before applying color and clear coat. Once finished and cured, mount using the factory attachment points. Ensure all fasteners are tight and check alignment before final tightening to avoid binding.