More correctly... the PK's (or in the case of hardware wallets, the "seed") should never be on an "online" device. Of course you should backup your hardware wallet "seed mnemonic"... but this should be "offline"... ie. on paper... or, in your case, the "air-gapped" laptop.
The problem with your proposal of generating your own PK's, as highlighted by achow101, is that you can't import individual private keys into a hardware wallet. So, you would need to generate a seed, and convert that to a 24 word BIP39 compatible "seed mnemonic"... you could then import that seed mnemonic onto your hardware wallet. Obviously, this would all need to be done on non-networked offline hardware. The methodology for going from a seed to a seed mnemonic is outlined in BIP39 (https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#generating-the-mnemonic)... basically generate 256 bit random number + "8 bit checksum" = 264 bits... split your 264 bits into 24 groups of 11 bits... each 11 bits = number between 0 to 2047 = index into word list of 2048 words (https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt)
In either case, paper backups of your seed and/or mnemonic are still a good idea in case of hardware failure killing your offline laptop.
The problem with your proposal of generating your own PK's, as highlighted by achow101, is that you can't import individual private keys into a hardware wallet. So, you would need to generate a seed, and convert that to a 24 word BIP39 compatible "seed mnemonic"... you could then import that seed mnemonic onto your hardware wallet. Obviously, this would all need to be done on non-networked offline hardware. The methodology for going from a seed to a seed mnemonic is outlined in BIP39 (https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#generating-the-mnemonic)... basically generate 256 bit random number + "8 bit checksum" = 264 bits... split your 264 bits into 24 groups of 11 bits... each 11 bits = number between 0 to 2047 = index into word list of 2048 words (https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt)
In either case, paper backups of your seed and/or mnemonic are still a good idea in case of hardware failure killing your offline laptop.
Thanks, that was a lot more clear. I think I now understand the pieces I was missing when I opened this thread.