Will this interfere with the trunk seal or brake light cutout?

This is a front lip under spoiler, so it sits well forward of the trunk and brake lights. No interference with rear body panels or lighting. Confirm clearance from any front bumper extensions or aftermarket fog light bezels before finalizing fitment.

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

Both methods work depending on your preference and reversibility goals. Adhesive (epoxy-based panel bond) is cleaner and non-destructive; drilling offers permanent security if you don't plan to remove it. Reference the factory bumper beam structure to identify safe drilling zones if you choose that route.

Will this lip stay stable at highway speeds?

FRP lips perform well at speed when properly secured and mounted flush to the bumper. Ensure all three pieces are tight to each other and to the base bumper—any flex or gap under aerodynamic load will cause rattles or worse. Use quality fasteners and test fitment before final installation.