You should change the order of packaging just Slightly. You've you skyboxes in the packages folder, but you should zip That folder and rename the zip rather than zipping a folder with that folder in it.

You should also try PNG file format, and there is a thumbs.db file to be removed in your jon folder.

Beautiful skies, they have great depth and you've given them the effect of distance amazingly well.
The one shown in the bottom left of the preview image doesn't quite fit with the rest of the pack, but its still good.