I think in the best technical way to get through without the agents being able to detect that you have a single satoshi. The most logical would be to memorize the seeds but relying on memory would not leave me 100% at ease. Is there another feasible, safe way
I really don't see any problem with paper wallets, hot/cold wallet on a phone, a seedphrase on a USD stick. I'm not sure where you're from, and I never seen this happening, so I really can't imagine them going through your phone apps. Is that even legal? Also, is this even something you have to do? I mean declaring your bitcoin holdings regardless of the amount being carried?