I understand that the Bitcoin QT wallet is already encrypted to some extent when I use a password. Is it best-practice to further encrypt the wallet file for long term storage?
From Bitcoin Wiki:
Wallet encryption uses AES-256-CBC to encrypt only the private keys that are held in a wallet. The keys are encrypted with a master key which is entirely random. This master key is then encrypted with AES-256-CBC with a key derived from the passphrase using SHA-512 and OpenSSL's EVP_BytesToKey and a dynamic number of rounds determined by the speed of the machine which does the initial encryption (and is updated based on the speed of a computer which does a subsequent passphrase change).
This means that it doesn't encrypt metadata or pubkeys. If you want to achieve a greater degree of security and privacy, I recommend to further encrypt the wallet file.