Will this interfere with the trunk seal or bumper fitment?

No. The lip mounts to the lower bumper area and does not contact the trunk or hood seal. The single-piece design sits flush when properly aligned to the factory mounting points.

What prep and finish work do I need to do before installation?

Sand the primer surface lightly with 220-grit or finer to help your paint adhere, then apply your chosen color coat or leave it primed. Once cured, mount to the bumper using the factory attachment locations.

Does this affect how low my car sits, or will it drag at speed?

The lip extends minimally from the bumper and is designed for street use at normal ride heights. If you run a lowered suspension, inspect clearance at your specific drop before final install. The FRP construction can handle typical road impacts, but extreme low setups may require additional care.