Hi John,
I'm on Debian 11.3 amd64, with Python 3.9.2 and virtualenv created by 'mkvirtualenv' (I use virtualenvwrapper). I use the standard path for virtualenvs, which is $HOME/.virtualenvs, and after my modification, the templates are now at

$HOME/.virtualenvs/roundup/lib/python3.9/site-packages/roundup/share/roundup/templates/classic/TEMPLATE-INFO.txt, and for the other templates respectively.

After creating the stuff you suggested, I end up with a virtualenv that looks like this, after installing roundup from mercurial:

$HOME/.virtualenv/roundup-test/lib/python3.9/site-packages$HOME/.virtualenvs/roundup-test/share/{locale,man,roundup/templates}, and under the 'templates' dir, I find the actual templates. At this point, roundup-admin does find the templates, but this directory structure does not look nice at all, at least not to my taste.