CHEAP FARADAY CAGE ?

[Highlander]

I would certainly double up on the foil on the outside box,.. but remember that the item inside cant touch the outside, so the item needs to be in a box of its own

One of the best Farady cages you can use on a budget is a metal dustbin, line the inside with cardboard, put your protected item into a cardboard box and wrap foil around it, and place in the bin, seal the top with the Aluminum tape,... I have done this, and placed the bin in a metal garden shed.

It will all depend on how strong the EMP is going to be, a single covering of foil might protect against a mild EMP strike, but best to try and protect against a strong one