Any thick, waterproof paint will work. Any device like this should be thoroughly tested before being used unattended. Heat it up without juice in it to be sure it won't burst into flames when it runs out of juice. The juice is pumped into a metal tube 4 inches above the iron with several pin-holes in it to distribute the juice over the hot surface. The heat vaporizes the juice into fog.
Unvaporized juice runs back down into the reservoir.
The intake for the pump is a metal tube glued to the side of the box with water-proof epoxy. It's bent 90 degrees at the bottom and the end is covered with a screen to keep little bits of junk out of the pump. The pump is mounted on the back of the box so it will be cooled by the flow of air. The fan and pump run on 12v, and the iron plugs in of course. A 15 foot control wire allows the operator to turn the fans on and off and the squirt the juice.