The liquid in Spirit levels has a nasty habit of drying up over time. Less time sensitive, is that they can be broken in an unfortunate bump. I would suggest mounting them in a way that they can be easily replaced. I have had two metal cameras; Linhof Technikardan (4x5) and Sinar P (8x10), and two wooden cameras; both R.H. Phillips (8x10 and 7x17). The Spirit levels were mounted with two or four screws of the same material used in other parts of the camera. The Linhof is sold, but the screws were a bright metal. The Phillips use stainless steel. I am not sure what is on the Sinar and I am reluctant to disturb the levels. It appears to be stainless, but I am not sure.