Roundcube plugins

[dfoy]

I have gone to the Roundcube web site and read through their instructions regarding installing and activating plugins. Unfortunately, they are 100% fixated on using Composer, and I am never, never, never, never, never able to get Composer to work. I desperately desperately desperately do not want to use Composer. So I upload and edit files using Filezilla and Terminal from my Ubuntu desktop.
I believe I have correctly configured my Vestacp Roundcube installation, but apparently not, because the plugins I want are not being activated.
Here is what I have done:
I downloaded the current Roundcube version which includes dependencies, and unzipped it. It includes a plugins folder that contains individual folders for each plugin.
I used FileZilla to upload the unzipped plugin folders from my desktop /roundcube/plugins folder to mysite.com/etc/roundcube/plugins
I downloaded the existing config file: /etc/roundcube/config/config.inc.php
I edited it locally so its plugins section is as follows:

// List of active plugins (in plugins/ directory)
$config['plugins'] = array(
'archive',
'zipdownload',
'markasjunk',
'carddav',
'filesystem_attachments',
'html5_notifier',
'jqueryui',
'managesieve',
'password',
'persistent_login',
'vacation_sieve'
);
I uploaded it again back to mysite.com/etc/roundcube/config/config.inc.php
I restarted my server. I logged into mysite.com/webmail.
None of the plugins are active.
Clearly I have made a mistake, and I would appreciate some suggestions about what, and where.