The wallet.dat of bitcoin core is already encrypted with a strong algorithm.
If you use a decent password you are safe to put your wallet.dat on a cloud service like dropbox.
A decent password should be 15 characters or longer, containing uppercase, lowercase, digits and special characters. Don't use anything written in a book or which can be found in an internet resource. Even if you change a few characters in such phrase, it will not be safe enough.
So you are saying if I encrypt my wallet from Bitcoin Core I do not need to PGP encrypt the backup file? That makes it convenient because I did indeed encrypt my bitcoin wallet from bitcoin core.
Exactly. For your interest:
http://bitcoin.stackexchange.com/questions/19975/how-secure-is-an-encrypted-walletPlease consider that you are vulnerable from the moment you connect your PC to the internet. If you trust the bitcoin-qt encryption, it doesn't matter where your wallet.dat file resides. Your PC can be hacked as easily as your cloud space provider.
For optimum security you should consider offline solutions like paper wallets or offline signing like trezor (or other hardware wallets).