Will this interfere with my trunk or bumper seal?

No. The rear lip mounts below the bumper without contacting the trunk lid or factory seals. Your trunk will open and close normally once installation is complete.

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

The rear lip uses factory mounting points on your bumper, so you'll secure it with existing hardware rather than adhesive or new drilling. This keeps the bumper intact and allows for easy removal later if needed.

Will this affect stability or handling at speed?

This is a visual diffuser, not an aerodynamic component. It adds minimal weight at the rear and will not impact your vehicle's handling or performance. Install it cleanly and it will sit flush at highway speeds without movement.