What a fantastic Question!
I wonder why no one has thought of that before.
Those defunct microwave ovens might be worth a lot.
Actually, the only thing that needs to be disabled is the Klystron (microwave generating) tube, and there you have it, a Faraday Cage for hand held communication devices, including cell phones. As long as it is plugged in, the unit is grounded through the three prong A.C. plug and everything inside the disabled microwave is protected from EMP.
I can’t take credit, I just was interested in verification. Storage for a solar battery charger, rechargeables, ham radio, walkie talkies, etc. Maybe a starter, alternator, coil, etc. for the Universal Jeep ... in case the bell rings.