Earthing question - plastic in metal?
The biggest credible hazard is that the wires to your "safe" kit
become damaged as they pass through the metal housing. If this is
not earthed, it could be nasty.
The protection provided by "double or reinforced" insulation ( which
allows the double insulation label and no earth wire needed) probably no
longer exists where the mains flex enters the "big tin can", therefore
the can should be earthed.
The mains flex will have insulation which is sufficient so that it can be
brought in close proximity to a tin can. Otherwise it would be unsafe to
touch. My main concern would be any sharp edges which could cut into the
cable, but even that could be overcome using grommets.
You need effective cable clamping too, otherwise a good tug on the cable
could roll out the grommet