How does one actually verify that the coins are indeed silver? Without access to the coin itself given the case needs to remain closed how does one confirm this?
Not sure if I would ever claim that something is "Tamper-proof" as nothing is tamper-proof if attackers are given enough time and resources to find ways around security mechanisms.
Other than that this is an interesting concept/project.

Just out of curiosity... How would you verify that they are silver if you had them out of the cases?
How can anyone "verify" that something is solid silver vs silver-plated?
There are acid tests, but you could also measure the coin's weight in troy oz. Using the normal volume of silver per mass this could be established. Of course I am no expert in this area but not having access to the coin at any point prior to redeeming removes any verification of the coin being actually silver.
I'm sure there are other way to determine this.