then write down the page numbers in a tiny notebook inconspicously in the order of the seed words.
why write the page numbers down? I don't think it would help, because you could just flip all the pages and find the words. It's only for convenience, but actually writting the page numbers on another notebook creates one more place where they could search. Besides, if you wrote down the page numbers (i.e 12 numbers), you could also write down the numbers of the words in the BIP-39 list (e.g. 291 for cattle, 103 for art etc).
The book should contain all 2048 words from the BIP39 list. I don't think it's worth all that effort. Furthermore, even if the book contains almost all the words that make up your seedphrase, you'll still be missing 4 to 6 words. You'll need to find another way to make up for this gap.
I don't see a better solution than steganography. It's very easy to hide information in a random PNG or JPEG image, but obviously you should encrypt the seedphrase first... the rest depends on your creativity.
If you're carrying a hardware wallet, keep it in your carry-on luggage, don't check it in, and if you're questioned about it, at most they'll ask why you're carrying this device and what it does. But you shouldn't have your device seized for this, I haven't heard of any country that restricts Bitcoin use or requires BTC declarations at customs.