Sorry, just now saw this. Yes, an ammo can is a good candidate for a improvised faraday cage. The lid overlaps the top of the can on three sides and the hinge runs the entire length of the fourth. I keep a ham radio in a plastic bag inside an ammo can as a "just in case" prep for EMP. The plastic bag is to ensure that it is insulted from the surface of the can (which WILL have a charge induced in it).