Given that the packages in question appear to be Free Software (at least
from a quick check of a couple of them, as well as the repository being
named "main"), is there a reason you don't maintain them in Debian
(including backports or volatile if you need to provide the newest
packages for older distributions)?
In my case I maintain open source software Debian packages outside of Debian because the software is far to volatile (e.g. important bug fixes on a weekly basis) and I don't want old versions hanging around any longer then absolutely required. It is also a very narrow market, possibly not of general interest to the Debian community (this is hard to determine however; maybe what this needs right now is expanded exposure).
There was also the (slightly confusing) perception in management that they had to tightly control ownership and distribution, despite it being open source GPL software, available on github, etc.
I note the original poster mentioned Ubuntu PPAs and add-apt-repository; my understanding is that these don't solve the trust issue, I seem to recall the user is shown a fingerprint and asked to confirm it is correct (based on what???) - however I don't have an Ubuntu box I can test this on right now.