Please: How is the booster fixed?

[gogo22]

Hi guys,

I have installed today the original Speaker Booster Blaupunkt BQA 80 in my '81 SC. Sound and volume is much better, even with the original head unit Bamberg QTS.

Where I faill is understanding how the booster is fixed under the passenger seat. I bought 91164504000 hoping it just come together naturally. Of course I could fix this somehow, but I would like to have it as original as possible.

Thanks a bunch in advance for any hints / pics.

Beat Gu