Yes, 19" rack-mount server chassis would be a perfect solution, but it is not mandatory. The previous best bet were ORWL devices but I never managed to use them because of several nasty bugs.

An idea to wrap equipment in some kind of a sealant is interesting, but I suppose that we'll face overheating problems in this case.

There is no need to automagically wipe data or to explode anything: sensitive data is protected by encryption, during system startup key are loaded from external removable storage. But I have to be sure that software was not tampered with while server was offline.