I found the thread, I will check it out. As the last act of resistance to you trying to crush my dreams, It appears to me the opening is wide enough you to get the plywood in. The arm rests seem to be the main potential problem. They don’t seem to be large enough and at the right location for wheels so I am thinking they have no reason to be there for 5 seater R1S (which is my selection). I remain hopeful. I may start my own don’t look up campaign (Reference to Netflix film).IIRC it is the narrowest point in the 3rd row per the SAE standard, which should be the further inward point arm rest in your second picture.
The first picture was from the LA Auto show, or around that time period. To the data I linked to earlier was apparently provided by CS a few months ago. I would suggest reading through that linked thread, we discussed the dimensions quit a bit in there.. also I recall a dedicated thread on fitting sheet goods, on my phone atm so not that easy to search for. When I get back to a computer I'll link to it.
Some more food for thought, just going by your second picture, you can think of the floor space available as the total width of the 3rd row. Is there at least 48 inches there? I would guess not.
Edit: worse comes to worse, I will rig something up to raise the floor and go over the armrest.