Will this lip interfere with my trunk seal or undercarriage?

No. The MS-R lip sits below the bumper and does not extend into the wheel well or rear trunk area. It mounts to the existing bumper structure, so clearance remains stock.

Do I need to prep or paint this before installation?

No prep required. The lip ships with factory clear coat applied, so you can bolt it on straight out of the box. If you prefer a different finish, sand lightly and apply your chosen topcoat.

Will the carbon fiber stay stable at highway speeds?

Yes. The one-piece design bolts securely to factory mounting points, and real carbon fiber provides the rigidity needed for highway use. Verify all fasteners are tight before driving, and inspect annually for any loosening.