A good way to go for hauling gear with those diminished tube boats is add a trailer frame. It adds another bay that can ride up/flex on the rocker a bit better than a straight frame that is too long. The front and back of those peaks beyond the straight section are pretty big and would accommodate a trailer frame nicely. The way that boat is rigged in the pic, I'd be inclined to pull the seat, move the towers and kick bar into the next bay forward, put a cooler or box where they are now, and slide the frame forward or back to the end of the straight and stick a trailer frame on for multi days. That would make it a pretty versatile rig. Make the trailer at least 18.5" so it can drop a row of rocket boxes in a drop bag and have a table over it. That'll keep your versatility up for big multi days where hauling rockets can be a big key.
Just my opinion from a rig that has worked well for me on a bunch of trips.