The drum is just a piece of 2mm thick stainless steel tube with ends welded up and axels put on. The 'teeth' are made by cuttings arks out of a larger tube which are then bolted on.
To save weight I could invest in some lipos and some of the Ali is getting cut away for the wheels and to make space for the drum. If worst comes to worst I could drill large holes in some of the bits of hdpe which are just there for support and don't act as armour. Finally I could downgrade to 2mm Ali baseplate and lid (would help with ground clearance) or see if i can find some cheap titanium. Or I could get a brushless motor to power it