ePADD was not originally designed for preservation, though we are continuing to add support for preservation with each release and the description I provide below may change in the future.
The current "Export to MBOX" functionality in ePADD 5.0 is intended to export an unprocessed MBOX version of email which may have been imported via IMAP, and includes all messages, including any messages you may have marked with restriction labels.
As you mentioned, the best current work-around available now to achieve your goal may be to export the mail to Delivery (since that does not include messages marked with restrictions, but should include general labels). Once in Delivery, navigate to the search screen. Leaving the search query blank, hit the search button. As you are working with a relatively small set of messages, this should return the complete set. From this screen, select the download button to the above-right of the message pane. This should download the set of messages.
Please let me know if you have additional questions!
ePADD Community Manager