Sorry i took it most of you would have seen similar types of builds to these before. Having been involved with caraudio since the mid/late 80s i sometimes make the mistake that people know certain things for granted.
Theres an infill section, then a cover that goes over them. As you can see in the photos the white parts are sunk in. These get grill/infill section and a carpet like material cover is then fitted on top. I did not see much point in showing these as all you will see is what looks like an empty boot

and i had thought most people would have prob seen similar to these many times before.
This is the infill on the second off last one i posted..

And the last one i posted.

cover fitted on top of last one ( I have not include the cover photo of the second off last one but its basically the same just fits better lol

)

As you can now see the boot is still usable.
The other advantage is its very stealth.