For anyone interested in modifying or increasing their rear cargo area. I removed my backseat etc and installed a platform to increase cargo area. This is a 23 EUV.
Here's what it looks like when done. Very solid and stable platform that can support a lot of weight.
Used sheet of OSB: 48" (front to back) x 38.125" (right to left) with two bolts holding it down. 19.75" carpet squares on top. Rubber backed squares don't need to be anchored down.
Those two bolts are all that is needed to hold it down. Heads are recessed so don't stick up in the way. They go in the seat belt bracket bolt holes. Bolts are M10 x 45mm flat head cap screws. Washers are 1.75" OD and 11/16" ID. OSB holes are 13/32" dril bit. Put the OSB rough side up (for traction).
Have to build a rear support out of two 35" long 2x4's. Glue and screw together in a "T" shape. I put self-adhesive Velcro strips under each end to hold in place. At the bottom of this pic on that flat seat belt support bracket/platform, that is where the two OSB mounting bolts go.
This pic shows all the 8 OSB lower support points. The furthest two white things are the rear seat hold down latches. OSB (luckily) sits perfectly flat on all these points, no wobble at all. Platform top is (again luckily) level in both dimensions. Thickness of the two 2x4's is 5". There is a large 5" high x (roughly) 36 x 36" area under OSB (from the 2 mounting bolts back) that you can store stuff in. My (deflated) spare tire does not touch the bottom of the 2x4"s.

OSB does not need to be screwed to the 2x4's. Again, only thing holding OSB down are those two bolts. I get no movement at all.

From the front of OSB to back of front seat (at my normal position) there is 11", so someone could sit there with feet down on floor with no back support. If you want to maximize the platform front to back length for sleeping or more cargo area you would add 9" to the 48" length = 57". This is an EUV, EV is less.

The area under the OSB in front of the two bolts is another storage space all the way from left to right side (38"). I store a lot of stuff under there as well.

In this whole process, no modifications were made to the vehicle, no holes drilled etc., nothing was changed. So, can easily remove platform and re-install seat etc.

Removing rear seat backs is a little tricky. There are other threads on this topic that are helpful. If you need help with that let me know.

If you have an EV (not an EUV) everything but the OSB length of 48" should be the same. Total cost of everything needed was about $20.

OSB does not touch any side panels, so no vibrational rubbing occurs. Trickiest part was where to drill the two holes in OSB. Had to use two laser levels. I have pics with dimensions but I have hit the Forum max byte limit so can't attach further pics. If you want these hole location details let me know. I can probably include in a response(?).

If you have any questions or need more pics let me know.

Bolterdash


Source:
https://www.chevybolt.org/threads/rear-cargo-area-mod.51689/#post-888107