Will this interfere with the stock splitter or undertray?

No. The lip mounts to the bumper fascia at factory attachment points and sits flush. Confirm your undertray clips or trim does not contact the lower edge before final tightening — most stock setups clear without issue.

What kind of prep does FRP need before paint?

Sand and prep the entire surface with appropriate grit for your primer choice. The piece ships without paint, so surface condition before primer application directly affects final finish quality. A clean, dust-free panel ensures color and gloss consistency.

Can I bolt this to the factory bumper cover without any trimming?

Yes. Designed to align with factory fascia mounting bosses. Dry-fit first to confirm all holes align before drilling any fasteners into your original bumper.