That's pretty cool! I've thought of doing something similar for my 2016 Odyssey but am too lazy :-)
Questions:
1. How does it bolt to the seat mounts (I assume) in the second row? Do you have a photo of that?
2. Doesn't the clamp scratch the seatstay? Surprised you don't use a clamp with a coating or padding of some sort.
3. What are the square box-looking things on the uprights of the rack? Cupholders, maybe? If so, bonus points for that!