I needed a way to encrypt files with GPG via the file manager (Thunar) right-click-context-menu in XFCE.

I came across this post that almost had it: http://ubuntuforums.org/showthread.php?t=578093

In Thunar, Go to Edit->Configure Custom Actions

Add a new action, call it “Encrypt” with the following command:

xfce4-terminal -x gpg –encrypt %f

That should work, and you can setup another one for decrypt.