Won't padding out the checksum cause issues down stream when you attempt to restore this in a wallet tho? 
It'll complain that it's not a valid BIP39 mnemonic. I know Electrum will let you bypass that and go ahead and use it anyway... but surely for max compatibility you'd want a "valid" mnemonic!
But yes, I was being facetious about manually calculating the SHA256 hash
... the setup you are using has a really good mix of "randomness", security and convenience. I like it.
It'll complain that it's not a valid BIP39 mnemonic. I know Electrum will let you bypass that and go ahead and use it anyway... but surely for max compatibility you'd want a "valid" mnemonic!
But yes, I was being facetious about manually calculating the SHA256 hash
... the setup you are using has a really good mix of "randomness", security and convenience. I like it.