/sys$common/syshlp/helplib.hlb PRODUCT, INSTALL, Qualifiers, /DESTINATION  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /DESTINATION=device-name:[directory-name]

    Specifies a location where the utility will install software
    product files. If you omit the device name, the utility uses
    your current default device. If you omit the directory name, the
    utility uses the [VMS$COMMON] directory as the default directory.

    If you do not use this qualifier to specify a destination, the
    utility installs the software in the location defined by logical
    name PCSI$DESTINATION. If this logical name is not defined, the
    utility installs the software in SYS$SYSDEVICE:[VMS$COMMON], the
    top-level directory for software product files.