We launched (forgive the pun) the SFTP service to upload packages securely to Ubuntu and PPAs a few months ago, but I’m not seeing much use of it. I would really appreciate it if more people would give it a go!
It also has the bonus that it doesn’t suffer from the bug where uploads sometimes hang with 1k to go, as on the regular FTP server.
Configure your dput.cf with these changes for Ubuntu:
method = sftp incoming = ubuntu/ login = <your LP account name here>
For PPAs it’s similar, just make sure your fqdn and incoming are set appropriately.
Let me know in the comments how you get on.