If you simply want to use bitaddress don't generate them there instead generate them to some trusted wallet like electrum as suggested above other suggestion is bitcoin core and Armory wallet run them offline including the bitaddress.
And then the private key that you generated from another wallet import it to bitaddress under wallet details and then enable the bip38 passphrase to add additional security/password then get the QR code under Private Key BIP38 Format and the key that starts with 6p.
You can later decrypt it on bitaddress just make sure never connect the device online to avoid leaks and always do it on an offline device.