You might not have a 5,000 lb. towing limit, depending on the weight of your fully loaded ERA. Your Sprinter has a Gross Combined Weight Rating (GCWR) of 15,250 lbs if your loaded ERA weighs more than 10,250 you will have slightly less than a 5,000 tow limit. Best to get your ERA weighed so you know your margins.
Towing a vehicle 4-down with a tow bar is no big issue. But you will need a system to activate brakes on the towed vehicle while towing and a method to integrate the parking and stop lights of the towed vehicle with your ERA Sprinter. Lots of options for each of these systems. I assume you know you won't be able to backup with the towed vehicle attached to your ERA. You will have to unhook to back up.
2013 Airstream Interstate Lounge EXT on 2012 Sprinter 3500 170Ext
Formerly: 1973 Dodge B300 DIY pop-top conversion