A two piece shell is employed for intermediate and long term storage of substrates. The shell is formed of two halves that can be juxtaposed in vacuum and externally vented, with the internal vacuum retaining the halves in vacuum-sealed engagement. One of the halves also provides a vacuum-sealing perimeter for selectively sealing to a process chamber during loading and/or unloading of the shell with a substrate. A vacuum monitor or the like may be employed to monitor pressure during storage and provide alerts if the vacuum within the sealed shell is compromised.