It’s an elderly caravan and if both sides look similar, albeit one has a crack, I wonder if the square section in the picture is for controlling sideways movement. When my OS axle rubber suspension failed it was only on one side where it extruded, Wheras the OP sides are similar except on square section has cracked. Not surprising as it’s nearly 20 years old. Also neither side has dropped its suspension height, Wheras mine dropped noticeably on the OS.
I would recommend having it looked at by an Approved Workshop Scheme dealership or mobile AWS technician.