Will this interfere with my trunk seal or door jamb panels?

The front lip mounts to the bumper fascia and does not extend into door or trunk areas. Verify clearance at the lip's forward edge before final fastening to account for any custom bumper modifications on your car.

Can I use adhesive instead of drilling, or do I need to drill through the bumper?

This piece is designed for bolt-on mounting to factory attachment points. Adhesive alone is not recommended for a front lip under load. Use the existing bumper bolt locations to secure the assembly properly.

How stable is this at highway speed?

FRP front lips are designed to handle sustained highway driving when fastened securely to the bumper structure. Ensure all mounting bolts are tight before extended highway use, and inspect periodically for any movement or flex that might indicate loose hardware.