Difference between air and water pressure

[GBJIV]

I was thinking about a related question.... When you here that a legal case is air tight. Is it better to be air tight or water tight? I guess it depends on the application. However, I recently bought a piece that I am thinking about keeping as BNIB for a long time - let's say 20 years. I am thinking maybe if I vaccum seal it in a bag i.e. remove air - maybe the watch, paperwork, Box etc... would not diminish as much. Should I ever want to sell it in 30 years.... It would be almost as if it was NOS.

Then I think it's too much work and not to worry about it either way...