Before we discuss the tow bar, I would like to ensure that you realize that if you tow this car, or any other car, you can without proper steps, destroy the transmission.
You may have noticed that there are very few "tow trucks" any more. They typically use a roll back flat bed and HAUL the cars to their destination. This is because the old tow trucks destroyed so many transmissions.
Most vehicles towed behind motor homes are either; front wheel drive towed on a front wheel dolly, vehicles with a means of disconnecting the transmission, four wheel drive with the transfer case set into the neutral position, or have had the driveshaft disconnected or removed.
I may be "preaching to the choir", if so I'm sorry. If you have not already researched this thoroughly, please do so to save yourself an expensive repair bill or a Benz going to the salvage yard.
I've never towed a Benz with a tow bar. Depending on the bar, you will probably have to raise or remove the flat rubber trim that extends out over the bumper. Connect the bar as close as possible to the bumper mounting points.
Best of luck,
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in