The ceramic or stoneware insert is the fragile heart of a slow cooker, while the heating base is nearly indestructible. Separate the two and pad the crock well, and this is a simple, low-risk pack.
Pro tip: If you are short on boxes, the metal base doubles as a sturdy outer shell, just add a towel layer between it and the crock before nesting them.
Watch out: Never travel with the ceramic insert still inside the metal base; the two knocking together under vibration is a common way the crock chips or cracks.