Polaris RZR 4 900 Complete Door Insert Kit. Door Inserts for the Polaris RZR 4 900, constructed from a powder-coated mild steel tube frame and plastic skins. We use a top quality thermoplastic high-impact polypropylene which offers a high-gloss finish with excellent durability and is available in several colors. These kits are an excellent option compared to the much more expensive OEM inserts. All hardware is included and inserts mount to stock locations on the RZR. No drilling required. While not designed to be water tight, these inserts do help a great deal in protection from from the elements and greatly enhance the RZR s looks.