[QUOTE=KneadToKnow]
My plan is to install one of those removable hard drive tray kits (example) and have two drives, one to keep off-site for security and one to keep in the drive for incremental backup, then swap them regularly.
[/QUOTE]
Those drive trays work ok and are faster than USB, but are less flexible; they won’t work on other PCs without opening them up.