Will these reduce my ground clearance?

No. Side skirts follow the rocker line and don't extend below the OEM ride height. Your approach and departure angles remain unchanged.

How do these mount — do I need to drill?

Mounting method isn't confirmed in the specs. Dry-fit both pieces before committing to adhesive or fasteners, and verify alignment with your rocker panel and door jamb.

Polyurethane vs. FRP — why choose urethane for side skirts?

Polyurethane flexes on impact instead of cracking. On a rocker panel, that matters — parking lot bumps and curb strikes are less likely to leave you with a broken piece. You trade some weight savings for durability.