Will these diffusers interfere with the trunk or rear bumper seal?

These are designed as add-on diffusers that sit below the factory bumper line. Verify clearance with your bumper's existing gaps before final installation — most fitment works cleanly without seal interference, but your rear bumper's exact overhang should be checked during dry-fit.

Should I use adhesive or drill through the bumper to mount these?

The two-piece design allows you to choose your install method based on your preference and comfort level. Adhesive mounting preserves the bumper, while mechanical fastening offers permanent security. Test-fit both pieces first to confirm mounting point alignment with your bumper's existing hole locations or flat mounting zones.

Do these need a clear coat, and will they stay stable at highway speeds?

Real carbon fiber benefits from UV-protective clear coat to preserve the weave finish and prevent oxidation over time. The hand-laid construction provides excellent rigidity — once properly secured, the two-piece design remains stable at speed. Sand and prep the surface before applying your chosen clear coat for long-term durability.