This is for the Chevy Volt shelf (https://voltshelf.weebly.com/the-all-new-voltshelf-g22-and-more-for-2016-19-volts.html) that can be used in a SECOND gen Chevy Volt. This is an amazing item that I highly suggest for Volt owners as it covers the large trunk from full sun exposure and prying eyes, as well as isolates it for less wasted heat/AC in an area that doesn't need it.
I disliked the metal brackets that came with the Chevy volt shelf, they would often snag, and when opening the trunk flip out of position.

So instead I opted to modify the two rear cover/net holding locations to be large brackets for the shelf to sit on.

These assemble with m2.5x6mm screws (8mm long works as well and may be better) and print in two parts because otherwise the forces of the shelf dropping on the part would sheer the print after a couple uses. It is a snug fit and may need to be slightly pressed into the opening before you can twist it to lock it. I used a pair of needle nose pliers to twist the stock ones out of place without breaking them.

This part does NOT have the little nub in the center for holding a net or the soft cover in the trunk, HOWEVER it does have a hole so you could alternatively hang them upside down and use a wooden dowel though them if you prefer that to hold your shelf in place.

I have not tested these yet in full summer heat. I'd suggest you print with PETG or ABS for better weather durability, the interior of a car can get hot in the summer with full sun a PLA print can and WILL start to sag with use if it gets too hot. either pulling out or dropping the shelf down into the trunk.

I printed mine with decent infill but more importantly I used thick walls (1.2 to 1.6mm) so that it would be more robust, and the screws would have more material to grab onto to hold the whole thing together.