Also, try and get some of those 'rip-when-removed' stickers and stick on the case. Put them in between where the front and back panels meet.
If the user tries to remove it, it will break and so you will know for sure that this has been tampered with.
Also, put a policy on firmware updates as well. Mention that updating firmware is at the owners risk because of many variations in firmware types and firmwares, you can not guarantee it will be compatible.