Hi Neil, I wanted to dig in a little more on your seat design, since I'm fascinated by the possibilities it opens.
Can I assume that the reel for the shoulder belts attaches somewhere to the backside of the backrest portion of the seats? I like that aspect as it frees the seat location to be independent of proper mounting positions on the van walls.
Also, can I assume most of the "box" under the seat is usable for storage? It seems like the linear actuator to raise the seat back will interfere somewhat in the aft portion, but there'd still be a usable volume there. I'm considering something similar but rather than using the electric actuator, I would just raise mine manually and then use a triangulating "arm" and pin it in place with a removable pin.
Thanks again for posting your wonderful images!