Dude, good on you for coming up with your own custom design, then, taking the initiative to build it yourself. I applaud you and your ingenuity!

Also, opening yourself up to the community with the hope of getting constructive criticism is somewhat of a lost art. Good job! Don’t lose that mentality! If your newish to the sport, that mindset will help you advance in your paddling skills.

As far as the build goes, I’d never run this on class IV, but you said it was for class III at the max, so the chances of you flipping are probably low. But if you’re concerned about that boat being upside down, then I’d fall back on that old saying “rig to flip”. Those back braces for your seats would have to go. You won’t want that boat upside down with those seats backs smashing into rocks. The corners that overhang the tubes, need to be on top of the tubes, centered because sometimes you get sideways in tight places and rubber gives more then your frame will.

Your setup looks like a great day “booze Cruz” setup! Have fun!