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?
They can search your electronics if you go through hard secondary (i.e. if you lie to them about the contents of your bag, where and why you're going and such).
Regular customs just a few seconds to get through, no more than a couple of minutes in case they ask you questions about your bag. Just tell them you have a hardware wallet in there, you don't have to tell them how much unless they ask.