I have been using them with great results for more than a decade. I have a Liberty safe, which uses cloth covered wooden shelves, with no problems. As others have said, mount at the bottom of the safe. They do get very warm for long term contact, so keep common sense distance away from your equipment. If you are in a high humidity area, it would also be wise to use a rechargeable Eva Dry or similar unit for extra help. Hope this helps...Stay Safe!