Create a query joining three Eloquent models

I have the following SQL query that I need to replicate using Eloquent:

SELECT SUM(COL.ORDER_QTY) as UNITS_SOLD, SR.NAME
FROM CUSTOMER_ORDER CO JOIN SALES_REP SR ON CO.SALESREP_ID = SR.ID
JOIN CUST_ORDER_LINE COL ON CO.ID = COL.CUST_ORDER_ID
WHERE COL.PART_ID LIKE 'MODEL%' AND CO.ORDER_DATE > '2018-05-01'
GROUP BY SR.NAME
ORDER BY UNITS_SOLD DESC

I created three Eloquent models for CUSTOMER_ORDER, SALES_REP, and CUST_ORDER_LINE.

CUSTOMER_ORDER

<?php

namespace App\Visual;

use Illuminate\Database\Eloquent\Model;

class CustomerOrder extends Model
{
    protected $connection = 'vmfg';
    protected $table = 'CUSTOMER_ORDER';
    protected $primaryKey = 'ID';
    protected $keyType = 'string';

    public function lineItems()
    {
        return $this->hasMany('App\Visual\CustomerOrderLine', 'CUST_ORDER_ID', 'ID');
    }

    public function salesRep()
    {
        return $this->belongsTo('App\Visual\SalesRep', 'SALESREP_ID');
    }
}

SALES_REP

<?php

namespace App\Visual;

use Illuminate\Database\Eloquent\Model;

class SalesRep extends Model
{
    protected $connection = 'vmfg';
    protected $table = 'SALES_REP';
    protected $primaryKey = 'ID';

    public function orders()
    {
        return $this->hasMany('App\Visual\CustomerOrder', 'SALESREP_ID');
    }
}

CUST_ORDER_LINE

<?php

namespace App\Visual;

use Illuminate\Database\Eloquent\Model;

class CustomerOrderLine extends Model
{
    protected $connection = 'vmfg';
    protected $table = 'CUST_ORDER_LINE';
    protected $primaryKey = 'ROWID';

    public function order()
    {
        return $this->belongsTo('App\Visual\CustomerOrder', 'CUST_ORDER_ID');
    }
}

How can I leverage these models to create the equivalent of the SQL query above?