Here's a total paranoid way of storing it. It was (and probably still is) used a lot for message coding by intelligence services of many countries, so old, but still effective.
Take a book. Any book you like.
Find all the words your mnemonic phrase contains.
Mark their location using page-paragraph-word number combination, ie 120826 would mean page 12, paragraph 8, word 26.
As a result you will have a series of 6 digit numbers which you are free to store on your Google drive, email to yourself or paint on your roof
Without knowing what the key book is no one will be able to decipher it.
Take a book. Any book you like.
Find all the words your mnemonic phrase contains.
Mark their location using page-paragraph-word number combination, ie 120826 would mean page 12, paragraph 8, word 26.
As a result you will have a series of 6 digit numbers which you are free to store on your Google drive, email to yourself or paint on your roof
Without knowing what the key book is no one will be able to decipher it.Actually there's a bit more to it than that.
Not "any book you like" but "any book you can get an exact page for page, word by word" copy of anytime in the future.
For example the first edition of Heinlien , The Moon is a Harsh Mistress."
First editions are really good for this purpose. For a famous book these are not going to be cheap, a couple hundred USD or so.