Specialty Recreation (SL1830S Smoke 18" x 30" Skylight Skylights are made of high performance thermoformed polycarbonate to be long lasting and easy to clean When choosing a Skylight, measure your rough hole opening as well as the overall exterior size There is a size to replace most manufacturer's original equipment Skylights sit directly on your RV roof Skylights include care instructions, and include a tube of approved urethane sealant that must be used when installing