Will this interfere with my trunk seal or undercarriage?

No. This front lip mounts to the lower bumper only and does not extend into wheel well or undercarriage zones. Confirm fitment against your bumper's existing mounting hole locations before drilling any new holes.

Can I use adhesive instead of drilling new mounting holes?

You can use adhesive as a secondary hold, but bolting through existing factory attachment points is the primary method. FRP adhesive bonds work best on clean, dry, sanded surfaces — prepare accordingly if you choose that route.

Is there any stability concern at highway speeds?

FRP lips are rigid by design and pose no aero risk at speed when properly mounted. Ensure all fasteners are tight and hardware is fully seated before highway driving.