They look like they are the packer plates. The instructions that come with the ARB outback drawers say for a 200 series, put 3X10mm under hat section A, 2 X 10mm under hat section B and also pack the corners. Outback make them for ARB don't they so yours would be similar in installation??? but may be a little different so I'd be contacting Outback because there's a cautionary note that says failure to install the packers correctly will cause the frame to flex.
If I was a bit smarter I'd copy and send it to you but it seems to be a locked PDF document???