Quoted:
Your electronics stand just as good a chance of surviving without buying a shipping container.
This is worth repeating. As protection against EMP, "Faraday Cages" are pretty much a complete waste of effort.
Basically, just about anything that's small enough to fit inside a shipping container is too small to be significantly affected by HEMP anyway. (HEMP is simply EMP produced by a high-altitude nuclear detonation, which is the only kind of EMP that's ever been demonstrated to be a useful weapon outside a laboratory - and thus is the only kind of EMP you'd ever encounter).
HEMP causes its damage by inducing high-voltage spikes in long electrical conductors (i.e., AC power wires, phone lines, cable/internet wires, large antennas, etc.). Basically, these conductors act like antennas - and the bigger the antenna, the stronger the "reception" of the voltage spike. In devices that lack any long conductors, little of the HEMP is received, and thus little voltage spike is produced inside the device. RESULT: The device is unlikely to be damaged.
What HEMP
does damage is electric utilities, phone lines, cable and internet connections, and other items that have long conductors. If you happen to have any devices plugged into these services, those devices are also likely to be damaged by HEMP. So, rather than spending time and money on something that doesn't do anything useful against HEMP, perhaps a better strategy would be to (1.) plan for not having utilities and other services available after a HEMP attack, and (2.) plan on either repairing or living without your damaged devices.
Additional reading:
Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack
Federation of American Scientists: Nuclear Weapon EMP Effects
Glasstone's Blog