Just a small bit of work this update. The original car body was a 5-seater, but with the added weight of the batteries it was turned into a 4-seater so it remained within the vehicle’s designed maximum weight limit. This was done by removing the rear middle seat’s headrest, seatbelt & installing a foam block.
The custom upholstered foam does block make a good arm-wrest for kids. And it stops “you’re on my side” arguments, too!
That’s all well and good, but that foam block meant I couldn’t fold the seats down since it was in the way. Which also meant I couldn’t fold the seats up for even more storage room. Nor could I even lay something flat across the back seat. That foam bump was always getting in the way. So, I removed it!
Seats out of the car. It’s amazing how much space there is in here! Enough to fit two dead bodies… because three would exceed the designed maximum weight limit. 
Geek Shirt #32 happened here too.
The reason why I had to remove the entire rear seat - the foam block wasn’t just stuck on top, it was affixed to this board placed underneath the upholstery.
Removed at last! You’ll never annoy me again
All back together. Now that the seats can fold, I’ll have so much room for activities!
One final thing - the upholstery foam is cream-coloured while the seat fabric is dark grey, so I placed some black electrical tape inside the holes to make them less noticeable. Black on dark grey stands out less than cream on dark grey. I’ve ordered some caps to finish this part off properly so it looks nice, but for now the increased utility is certainly welcome!