Cover plates are provided for use on deck. A cover plate is used together with a high quality sealant to create a waterproof seal. We recommend you check this seal every four to five years by removing both the cover plate and chainplate. If there has been water intrusion, it will damage the plywood deck core as well as the interior main bulkhead. A chainplate that is kept in constant with moisture by the the saturated wood in the deck is also subject to crevice corrosion and failure.