An enclosure device has a protective cage shaped to fit around a marine drive unit of a boat, and trailer mounting elements adapted to be mounted on a trailer carrying the boat. Pivotal elements pivotally mount the protective cage on the trailer mounting elements so that the protective cage pivots between a lowered position wherein the protective cage is beneath the marine drive unit and does not interfere with offloading the boat from the trailer, and a raised position wherein the protective cage at least partially encloses the marine drive unit. A locking element may be used to lock the protective cage in the raised position.