EMP

[Lightspeed]

Metal lidded, plastic lined chest freezers work well. ( And can be picked up dead for free from neighbors etc)

Bond the lid to the main body with Coax antenna wire screen.

Plastic lining insulates the contents from the outer metal wall.

Paul's test is a good one. If mobile phones and CBs are not receiving, that proves no EM radiation between 27Mhz and 900 Mhz is getting in.

I don't think that a Faraday cage needs grounding to work effectively, but others argue strongly for grounding.....if you want to ground it, its easy with a dead Chest Freezer: strip out the live connections in the 13a plug, leaving the earth, then just leave the plug connected to the mains and it'll earth through the ground pin.