Sweet rig, you've obviously put a lot of thought and time into it. Want to do my frame next?
With all that black foam, you'll definately want shade if you're not in the rapids. I sport these guys: River Sombrero - Shade for Rafts!
, get the 8' and remember to fold it up before you get to the top of the tongue.
If I follow, you're sleeping 2 people long ways on the boat. That is going to feel really narrow when you're trying to spread out in the heat. Your height of the boxes above the plywood looks close to an ammo can. I would look into how you can strategically strap cans, bags, and anything else along the side rails, and then get a couple of thick white paco pads that will cover up the bumps. Spreads you from 40" to 60"...
I wouldn't trust any cooler latch in a flip - if it were me, I would still cam strap over the top for rapids. Even just one in the middle... That's a great rig for lower-key stuff though!
Happy tinkering, and have a great trip down there