To work best, the Goldenrod should be on the floor of the safe so that convection will warm the air throughout the safe. It's also desirable that the unit be mounted at the front of the safe, so warm air can flow easily up to the top shelves. If you've put your gun safe in the basement, you might consider getting a room dehumidifier to assist the safe dehumidifier. Interior Lighting Lighting inside your safe is absolutely necessary - you have to be able to see when your rooting around inside it looking for something. The safe doors with interior hinges I've seen only open ninety degrees, and that blocks light as well.
Many safe companies sell brass piano-style lights to be placed atop the safe.
Others sell a fluorescent lights that mount along the inside of the door. The real problem with lighting a gun safe interior is that there are so many shelves, walls, racks, guns and other valuables inside that any light source might illuminate one area well enough, but leaves the rest in shadow. The only solution is the use of many lights. The local Home Depot sells bookshelf lights of various lengths. The shorter I put inside the roof of the safe, as close to the front as I could manage.