Get some physical tamper detection on opening the case. Something like the old spy trick of 'leaving a hear on the door-handle'. There are some nice tips here

Get some physical tamper detection on opening the case. Something like the old spy trick of 'leaving a hear on the door-handle'. There are some nice tips here on spray glitter on a seal and nail-polishing it, then taking a photo. That way, anyone that breaks the seal has to reproduce the same glitter pattern.