Dear Chris,
There is a possible conflict/collision for a URL structure without using the post type slug. By default, WP does not allow this by design because the post type slugs are there to isolate one post to another and to provide a sense of grouping. This is important for search engines and other indexing algorithms.
Have you manage to get it fully working? Yes combining the custom permalink plugin and the one I've suggested is fine as long as it does not return redirect loops, 404 and PHP errors throughout your site. I recommend to use Xenu: http://home.snafu.de/tilman/xenulink.html to crawl your site locally in order to find broken links and redirect errors after development. I find this useful when I'm doing some major URL changes before.
In addition, I find the following links from Google, probably it can help you other working solutions:
http://vip.wordpress.com/documentation/remove-the-slug-from-your-custom-post-type-permalinks/
http://wordpress.org/support/topic/remove-permalink-slug-from-custom-post-type
Cheers,
Emerson