“That is also why the inside must be lined with something non-conductive. If the contents inside are in contact with the metal walls they are subject to the EMP.”
No, that’s not correct. The metal container acts as a Faraday cage which do not allow the electromagnetic pulse radiated signal to penetrate. What is important is that it is a good conductor (like aluminum) and that there are no openings or gaps which can act as slot antennas and allow EMP penetration. Everyone knows that if you’re in a fringe cellular area, you’ll get a better signal if you get out of your car - that’s because the car is acting as a poor partial Faraday cage and only permitting microwave signals from the cell tower to enter via the glass areas. Think of an armored car and you’ll be much closer to a good EMP shield and be unable to get a cellphone signal at all.
For the lazy and/or paranoid who want to protect their small devices against the chance of an EMP while they’re out shopping or whatever, just put them in your microwave oven (don’t turn it on!) Microwave ovens have to be very effective Faraday cages to contain the high power microwave energy that would otherwise cook or neuter you, and they work equally well at keeping electromagnetic radiation OUT as IN.
So just build yourself a giant microwave oven-like room. They’re all over industrial labs, known as “screen rooms”. Screen is effective as long as the openings are small enough that energy of the frequency of interest cannot penetrate.
To avoid accidents, please unplug your microwave before you put your cell phone in!
You will have to argue that with the engineers and the military. Every paper I have read, and I have read many (can link some but not on this tablet) has clearly stated that and the military equipment cases always set their equipment in non-conductive foam.
Here is an article by Jerry Emanuelson, B.S.E.E: Getting Prepared for an Electromagnetic Pulse Attack or Severe Solar Storm
A locking-lid galvanized metal trash can, though, can be a very effective electromagnetic shield. Although it can be very effective, it is less than perfect, so the interior of the body of the galvanized metal trash can should be lined with some material to electrically insulate items stored inside the container from the metal exterior. (Cardboard probably works better than any other inexpensive material for this. Liners such as plastic trash bags may be too thin for this because of the momentary high voltages that could be induced on the exterior of an imperfect faraday cage during an actual EMP.) . . . (contact) may simply conduct the EMP energy into the (protected) device more effectively.This is a page about some of the things that individuals can do to prepare for an electromagnetic pulse attack. I'm an electronics engineer who has been thinking about the EMP problem for more than 3 decades.