Bank's storage can be a valid place since it may be opened only by you or with your death certificate, afaik.

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I thought the whole point of Bitcoin is be your own bank. If you have to store your seed in a bank storage, what is the point of having Bitcoin in the first place?
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alexkrypto, I couldn't agree with you more.  Don't let all the hate you received on this post deter you.  It is not 100% clear to me how the "mnemonic phrase" and the "password phrase" get used in creating the final bitcoin private key and addresses.  I get that if no password were involved the 3-word mnemonic phrase would produce a less secure private key then a 6-word mnemonic phrase.  And I get what you are trying to achieve.  The whole point of bitcoin WAS so we wouldn't have to trust and use the banks!  I support your efforts and desire to completely cut the banks out of your life as much as possible!  Especially after how irresponsibly the FED has behaved this past year!  They can all... well I better not say.  But I am totally with you!  I have developed several methods myself and got a lot of hate when I tried to clarify certain aspects of my ideas as well.  I don't understand why most bitcoiners seem to think we have to walk the straight and narrow on proper protocol for securing your private bitcoin keys!  I think the metal plates to stamp your mnemonic keys into are stupid!  Unless the mnemonic key is encoded first!  None of my mnemonic keys are written down in the right order or even the right words.  Everything I do is encoded one way or another. I use mis-direction.  I use all kinds of methods!  The government nor the banks will ever get my crypto!  I am working on leaving some information that is written down behind for my kids after I die.  But they will first have to get the decryption keys that I will leave with my will.  Those will only decrypt the documents that explain where they can find the jump drives and other documents and decryption keys to finally decrypt the documents that will explain how to decrypt my mnemonic phrases.  Hopefully they will be able to properly follow the trail of breadcrumbs.  If not.  Oh well.  I'm not leaving my fortunes to the government or banks.  And if my grandkids are too stupid to figure it out.  I don't care if they get my money.  There will be a clear trail to follow.  It just won't be a trail that the Lawyers handling my will or the government will be able to follow.  Because you'll have to know certain things about me and my family.  About my past and whatnot.  Call me crazy!  I don't really care.  Carry on with your innovative ideas!  Nothing wrong with what you are trying to achieve.  I have several bitcents (0.01 BTC) stored in bitcoin addresses that exist ONLY IN MY HEAD.  I have written down some information that when properly decyphered will allow a family member to re-create the private key but I don't actually have the private key written down or stored anywhere.  Not even the mnemonic words.  Nothing!  It's all derived from information that I can remember easily and given a few hours I could sit down and reproduce the private key.  I have method to my madness.  I get that it's possible I could have a stroke and forget.  But I like the idea that if I were suddenly to find myself in a foreign country and needed funds.  I have them with me.  In my head.  All I have to do is find a bitcoin ATM.  Damn cool if you ask me!  And if those 7 or 8 bitcents get lost forever.  Oh well.  I've just increased the value of everyone elses bitcoin.  You're welcome!

I'd be happy to continue this discussion with you privately if you're interested in more ideas.  I'm not going to give away what I am doing but I think it's fun to discuss ideas of how bitcoin can be hidden in plain sight.

And for the record.  The first word of each sentence isn't that secure either.  Especially when there are exactly 24 random sentences???  I mean really?  The fact that they are random and disconnected would immediately make me suspicious that they were a mnemonic phrase.  I think there are better ways to disquise which words in a given paragraph of writing are the mnemonic words.  The writing should make sense.  There could be punctuation marks or just random things that would make the mnemonic phrase much less obvious. 

O.K. I'll get down off my soapbox now.  All the rest of the people in this thread of posts who think the OP has to write all his phrases down correctly and store them in a bank vault can leave now.  You can do what you want with your hard earned money.  I'm not trusting a bank to keep mine safe.

Kresp