Will this interfere with the trunk seal or lower bumper fitment?

No. The lip is designed as a bolt-on extension to the lower bumper; it does not contact the trunk or side panels. Verify clearance by test-fitting before final fastener installation, especially if you have aftermarket suspension that changes ride height.

Does this lip cover or interfere with the brake light cutouts?

The lip is positioned on the lower fascia and does not obstruct factory lighting or sensor openings. If your vehicle has been modified with non-factory bumper holes or sensor placement, confirm those locations are clear of the lip extension before permanent fitment.

What's the best way to prep the FRP for paint?

Sand the entire surface to remove the glossy gelcoat and create paint adhesion. Wipe clean with a tack cloth, then apply your chosen primer and topcoat system. The raw FRP condition means the surface is receptive to standard automotive finishing — no special prep treatment is required beyond standard sanding and cleaning.