gpg is great, but its compression isn't the greatest and pki is overkill given you are both the sender and consumer of the data.
how about using 7-zip? (
http://www.7-zip.org/ ) - its free, you can script it easily enough, you can split the resulting archive into chunks if that makes life easier, and when used with a static password, it encrypts with AES@256 - which for gpg would be best-case (normally gpg uses 128 bit crypto)
