Things we need to avoid while storing the Private keys are -
- Never print on a paper or take a photo of a seed.
We can store the seed using a paper wallet, the cheapest, and the best way to hide the seed.
How can you claim that storing the seed printed on paper is insecure, while at the same time recommending a paper wallet?
Storing the seed on a piece of paper is not insecure by definition. However it depends on the thread model, as always.
If an evil maid scenario is possible for you, storing it in plaintext on a piece of paper is insecure. If your physical storage however is safe, that's not the case.