Will this interfere with the trunk seal or latch?

No. The under-spoiler design mounts below the bumper line and does not contact the trunk assembly or weatherstripping. Clearance is maintained for normal trunk operation.

How stable is this at highway speed?

The F-1 profile is designed to generate downforce, which increases stability and traction under acceleration. At sustained highway speeds, the added grip benefit becomes noticeable, especially in cornering.

Can I drill through this for permanent mounting, or should I use adhesive?

FRP handles both methods well. Drilling through the flange areas is common and gives you the strongest hold; pre-drill to avoid stress cracking. Adhesive-only installation works if you prefer zero drill points, but mechanical fasteners are more reliable long-term.