Currently if you want to backup/save closed Submittal items externally, you need to export report and download attachments separately. No way to action some bulk export of all if you need them for As-Built/ O&M Manual, which you need to upload to Clients repository/server etc. Very frustrating as takes lot of precious time for manual work.
Please consider some solution for exporting an item alltogether with attachments (and its markups if required), the best in some bulk option.