Will this diffuser scrape on steep driveways or inclines?

The wave-profile design extends beyond the OEM bumper line. Verify the exact extension against your local driveway grade and approach angles before installation. Most owners with stock suspension experience no issues on standard residential inclines.

Does the diffuser require the OEM rear bumper to stay on, or is this a full replacement?

This is a diffuser add-on that mounts to the existing rear bumper. You retain the OEM bumper structure; this piece attaches to the underside area. Confirm mounting hole alignment with your vehicle's current bumper before drilling.

What prep and finish should I use for raw FRP?

Sand the surface with your preferred grit and clean thoroughly before applying primer or paint. FRP accepts most automotive primers and finishes. Test your chosen paint system on a test panel first to ensure adhesion and compatibility.