How do I augment the Cartalyst Sentinel Sign Up/Sign In functionality?

Question

I am trying to learn more about Cartalyst Sentinel in Slim PHP for user sign up and authentication. I'm a bit out of my depth as I've not attempted this type of thing in the past.

I have been following this tutorial on how to implement Sentinel in Slim:

Removing the Pain of User Authenticaion With Sentinel

I have everything working as explained, however now I want to start changing things a little to require additional data captured at the sign-up process; a username, date of birth, country selection.

I have added the additional columns in the users table, and added the required form fields and updated the code in the controller:

    $user = $app->container->sentinel->create([
        'first_name' => $data['firstname'],
        'last_name' => $data['lastname'],
        'username' => $data['username'],
        'dob' => $data['dob'],
        'country' => $data['country'],
        'email' => $data['email'],
        'password' => $data['password'],
        'permissions' => [
            'user.delete' => false,
        ],
    ]);

However no additional data is stored in the database table. From some further reading on the below link by Naomi Aro it seems like I need to update the the Users Model, which I've done, but dont believe I've done correctly!

Multiple Login Attributes with Sentinel and Laravel

namespace app\models\Users;

use Cartalyst\Sentinel\Users\EloquentUser as SentinelUser;

class Users extends SentinelUser 

protected $fillable = [
    'email',
    'username',
    'dob',
    'country',
    'password',
    'last_name',
    'first_name',
    'permissions',
];

protected $loginNames = ['email', 'username'];

I've required my model in the index.php file but it doesnt seem to be picked up, so I assume I'm not implementing it correctly with Sentinel?

$app = new \Slim\Slim(array(
    'users' => [
        'model' => 'app/models/Users',
    ]
));

I also found this post which deals with the same issue, but is Laravel specific.

Laravel Cartalyst Sentinel - Adding a username column to users table (What is the right way)

I'm not sure how to proceed, does anyone have any idea or suggestions?

Thank you!!