@OP you don’t need to use SlickStack in order to use RepoMan, and you can still install RepoMan as an MU plugin if you really want in whatever existing web hosting environment your clients are using… unless your web host cleans/deletes MU plugins automatically. Some web hosts will automatically reset the MU plugins every day for example but if your web host allows you to modify those, you can just upload and install RepoMan under the /wp-content/mu-plugins/ directory and leave it there long-term