PowerArchiver has a UUencode/XXencode/MIME tool which can be used to conveniently encode files in UUe, XXe, MIME (base64) and yENC formats.
To use this tool, first open an archive in PowerArchiver that you wish to encode. Once you have opened an archive, select "Encode…" from the "Tools" menu, or press "CRTL+D".
The UUencode/XXencode/MIME/yENC dialog box will appear, and you will be able to select the destination file and method of encoding. As an added feature, you can also choose to make multi-volume encoded files with the spanning option.