Walk in refrigerator room

Walk in refrigerator rooms do not need mezuzahs. This is regardless if they are 4 by 4 amos (37 square feet). The reason is since it is not a room fit to dwell in. Some are extra strict to place a mezuzah on these rooms (without a blessing) since if the electricity would turn off one could dwell inside, but vast majority Rabbonim do not accept this claim.

Metalic Mezuzah cases

The Baal Shem Tov was known for not using a metalic case to hold a Mezuzah. Explaining that metal is intended to shorten the length of man while a Mezuzah scroll is to lengthen the life of man. The Daas Kedoshim writes, that this carefulness did not apply to silver, however the custom was not to use them since they were more likely to being stolen. Apparently the Chabad custom is not to use even silver even if we are not suspecting it would be stolen, for example a silver mezuzah case inside the house.

I asked Rabbi Levi Yitzchak Raskin (Dayan of Lubavitch community in London) that in his book (Nesivim Besadeh Hashlichus) p. 94 he wrote that the chabad custom is not to have silver or other metallic on the mezuzah case would that also apply to a tiny design like in the (right) picture posted?

He answered: "I WOULD NOT OBJECT. IN A 'DVAR CHIDUSH' I TAKE THE APPROACH "אין לך בו יותר מחידושו".