The slit cover does slide on. It's a rolled steel frame with aluminium support and polycarbonate skin. The walls are colorbond on galvanised steel. The actual base is rectangular so you can have a table/cupboard tucked away under one end. The walls and ring support just bolt together.
Some earlier photos:
http://www.iceinspace.com.au/forum/s...d.php?t=109221
It served me well for 20 years.