What is the Metal Covered Tank in the rear of an RV of the Roadmaster BrakeMaster

I have the Roadmaster BrakeMaster w/ BrakeAway and Pressure Reducer - RVs w/ Hydraulic Brakes on a Georgetown I recently bought used. I had the brakes transferred from the previous owners vehicle to mine you answered this questions previously and works fine. Just wondering what the mechanism is that is in one of the rear bays of the MH that is related to the brakes. It has a metal cover around it so hard to see what it is. Is this an air tank? Does it have a pump if so Ive never heard it run? Does it supply air pressure to the or vacuum tow vehicle brakes? Thanks

asked by: Tom