I put 9 sheets of 2mm silent coat on the load side of the bulkhead, spaced a few inches apart and carpeted the cabin side with the mega stretch carpet from Mega Van Mats.
The carpet is trapped at the edges between the bulkhead and the fastening points as well as having some trapped between the two halves of the bulkhead.
It's nice and quiet now and the cabin sounds more car-like. If you tap the bulkhead it sounds more like thick plastic than the previous metallic clang that it had.
I took the bulk head out and carpeted the two halves separately. The carpet does catch on the bolt ends when putting it back in, so it's worth scissoring the holes before refitting.