Will this interfere with the trunk lid or rear bumper seal?

The W-1 profile is designed to sit cleanly under the bumper without contacting the trunk seal. Before final installation, test-fit the piece to confirm clearance with your specific bumper — minor gaps or trim may be necessary depending on how the original fascia sits.

Can I use adhesive, or do I need to drill mounting holes?

FRP diffusers can be mounted using either high-strength automotive adhesive or through-bolted fasteners. Adhesive alone works well for highway use; if you plan track days or frequent removal, drilling through-mount holes into the bumper support provides more security. Choose the method that fits your use case and intended permanence.

How stable is this at highway speeds?

FRP is rigid and holds its shape well at speed. Once properly mounted and cured (whether adhesive or bolted), it won't rattle or shift. The key is solid mounting — avoid partial adhesion or loose fasteners, and the piece will stay planted through normal driving conditions.