Had lost some items in the small pull open storage area under the drivers side rear seat. Popped the seat top off to recover the items and found a good sized storage volume there. You would have to isolate items to that side since under the other seat is some equipment that would need to be protected. But for seldom used items that you might like to carry, like a real hydraulic jack for spare changing, or extra emergency clothing it could be useful. The seat just pops off from 2 clips and goes back on easily.
I checked out the space under the seat today. The seat bottom comes off fairly easily, just pull up on the left edge to release the first clip, then pull up on the front edge to release the second clip. The seat bottom is super light weight! There's an area behind the car jack that I suppose could be used for storage but you'd have to be careful that nothing slides around.
I believe that the ''extra space'' you found under the seats is filled with more equipement on the Primes equiped with the solar roof (Japan/Europe) , the auxilliary batttery is hidden in the armrest and the controller must be under the seats. Also don't forget that the Japanese version include a chademo connector ... so more stuff ..
Currently remaking it with some mounts but basically I moved the inverter I had from the engine bay to under the rear seat. When I get a chance I'll draw up a diagram and take some pics.
Hi Mikhail just wanted to bump this again as I’m very interested. Thanks! On second thought ignore it. I’ll try to be more patient.