Personally I'm thinking to store all my wallets on a metallic plate (QR code) and copies on plastified paper. I want to store the first in a safe-deposit box in my bank insured for 30.000 € - even if the value of my wallets in theory could be greater - and the latter in a secret and inaccessible place that even CIA can't find As if it isn't enough I'm going to use my personal "system" for the letters and numbers wrote on the paper.

Frankly I don't understand why people don't use safe-deposit box. For less than 30/50€ per year you can keep your box in the vault of a bank. 1 key is for you 1 key is for the guy with a gun that lives in the vault. Evey time you enter you have to sign the attendance register. If your box is stolen or if the bank cannot find it (e.g. earthquake, meteors etc.) the insurance company have to pay out 10-30k (or even more) immediately with real money even if your box was empty. Way better than an USB device in my opinion.

p.s. Yes, I am a bit paranoid