Both of Robert's script "Secure-Wipe" & "Encrypt/Decrypt" work like a charm in Thunar!
Simply copy both scripts to seperate files in any folder you would like, then open Thunar & set up "custom actions" for both, then simply point those to the script files that you had just saved.
Only one issue with the "encrypt/decrypt" script, for some reason when decrypting the file, the decrypted file never actually appears, even though the info-box says the decryption is complete. Just double-click the file & you can decrypt with the default GPG program.
Don't forget to "chmod" both actions in a terminal window.