I rigged this up in about an hour yesterday I only have a jet sled XL and it gets stuffed pretty quick so I needed additional storage for buckets etc and somewhere to mount my shanty. I took a board measured out the length to fit a couple milk crates, got some 175 lb zip ties and some eye bolts and big washers I attached the board through the two holes I drilled in the rear rack, ( circled in red) the big eye bolts went up through the holes I drilled in the rack to the board. I now have additional attachment points to strap my quick fish down, to attach the milk crates I just drilled 8 holes 3 sideways and one set going across the other 3. zipped it through the holes I drilled now 4 are holding on each crate they seem rock solid as does the board.
In the blue bag is a socket set and first aid kit, I didn't want to cover the factory rack because I wanted a space to keep the blue bag and still need access to the rear of the seat where I keep other tools, belt, plugs, pliers, rope, etc. I have a tackle bag for lure storage it will fit perfectly between the crates and it'll be held sideways by the crates and the shanty to the rear, when I strap the shanty down I'll go over the top. The bungies are there ready for use. Next season I'll most likley get a flip over so I may just add a 3rd crate and put a new board on, gonna work in a pinch for this weekend though.
I hope that makes sense. Here are before and after pics