A 6" long piece of 2"x2" 90° angle iron bolted to the core support. It was used to hold the battery in place along with a bungy cord. Expanding foam insulation used to fill holes in the trunk. The PO of my cammer was a real bone head.
When I pulled out the carpet in my convertible, I found an unused trunk key on the passenger side floor. It was under the jut insulation.