Lutz......what is that item to the immediate right of the wood box? Can you post a closer pic of it?
As far as your sine plate....spray a rag down with WD-40, and spray the foam inside the box with WD-40. Keep the rag on top of the plate. This will prevent any rust from starting on them from any humidity. I have a compound sine plate that has been sitting on my bench or shelf for a few years now, and I keep a rag that has been soaked with WD covering it, and so far, no surface rust at all.
BTW....if you don't mind saying, what did you have to pay for the machinist tools?