i think he is talking about a safebox in his house, he can control it easily if he know the combination
That's a horrible idea, what if your house is broken into and someone grabs your lockbox? you pry those things open in seconds with a crowbarI honestly believe my methods are the safest possible:
For my hot wallet I use my Trezor, for cold I use paper wallets and store them in a safe deposit box ( insured! 
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I also keep my recovery card in my safe deposit box
)I also keep my recovery card in my safe deposit box
safe deposit box can be broken as well it's not they are immune to thieves, the big thing to have when you hold plenty of money isn't the security of it but the awareness of the people about it, in other word don't tell to anyone that you're holdin a big amount and you're safe
It doesn't matter if my safe deposit box is robbed, that's what the insurance policy is for. I make a claim and get my money back. It's much safer to keep your paper wallets at a bank versus hiding them somewhere inside your house.
If you had that deposit box in Japan, then the insurance probably wouldn't pay out as Japanese law says a Bitcoin doesn't even exist and therefore you cannot be compensated for something that you didn't lose in the first place.
Bearing in mind all the new laws that are shifting around crypto, I wouldn't trust any insurance company to pay out. Insurance companies make their money with clauses and slide-rule identification at point of claim.
If they can find a law that means they don't have to pay out, they will.