@bone - great job on your installation. Thanks for sharing your work.
I too captured this storage space in my 2015 cargo with a different approach.
I couldn't stand the vinyl cargo mat so used carpeting on plywood instead.
I separated the foam from the vinyl mat and used that as filler under the plywood, which is very good sound proofing material.
It's great to have the extra storage space making use of this dead space.
Time for you to finish those bare door panels next!
I used black paint on mine. Gives the van a nice finished detail.