It spiraled a little out of control due to misunderstanding.

Back on topic about hiding private keys. I remembered how I kept some notes hidden when I was little. I disassembled pen and made little scroll out of pittle piece of paper. Then I would put it in pen's tube and assembled pen back together. If the pen has opaque tube it will be pretty hard to discover the note.

If I would be really paranoid I would use lemon juice to make invisible ink and write seed words with it. After arrival to destination I would recreate the wallet. By applying heat from the lighter seed words would appear and it would be possible to write them in wallet app.