Do I need fasteners to install this, or does it come with hardware?

The diffuser ships as the panel only. You'll need to source appropriate fasteners based on your existing bumper mounting points. Reference your vehicle's OEM rear bumper attachment locations to determine bolt size and quantity required.

What prep work should I do before painting?

Sand the surface with progressively finer grits and clean thoroughly to remove all dust. Apply a quality primer designed for FRP composites, then topcoat with your chosen color. This ensures proper adhesion and a finish that matches your vehicle's panels.

Will this fit if I still have the factory rear bumper on my vehicle?

You'll need to verify clearance between this diffuser and your existing bumper cover. Measure the mounting points on both your OEM bumper and this panel before installation. Some fitment may require minor trimming or spacer use depending on your specific setup.