I have done lots of work for agricultural facilities that contain greenhouses. They are definitely damp locations, if not a wet location with the use of sprinkler systems verses bed watering tub systems. The other concern is temperature derating of the current-carrying capacity of the conductors used to feed equipment. Sealtight (Article 356) and PVC (352) has always been the best choice for me. W/P connectors, boxes, and devices are also a must. Good Luck!
Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter