Gen 3 Cargo Liner
The black tray that you're discussing came with my Gen 3 when I bought it used. The PO told me it was a Dealer Installed Option. I found a Part # CTT 4011 on the bottom side. It doesn't look like a Toyota factory part # so I assume it is the vendor part # and probably decodes to Cargo Tray Toyota #4011. I ran this in google a couple ways and did not find any references.
It is medium thickness and very nice. Mine came with 6 12-15" long divider plates that clip in longitudinally to holes to arrange/secure grocery bags or luggage, and a longer divider that is about 20" long that inserts laterally for more variety (in your pictire, you can see the slots it goes in about 1/2 up. The 12-15" dividers clip into holes that go all the way thru the tray so could be a source of water leak if you put something wet in there. Maybe it will hold 1.25-1.5" water before spill over. I know from use that the dividers rattle when you drive so I store mine out of the rig and just put cargo in it like you have it pictures. Thats about all I have for you. Hope it helps. I love WeatherTech and Husky cargo liners but won't replace this tray as it handles the job for me. Good luck in your search.