I found an adjustable rack, just two supports going down and they were a rod inside a tube with three holes to make the different lengths. I had to cut the tubes shorter and drill new holes to make it fit just above the 12" wheel. Axiom Columbus bag on top that is insulated to be a cooler. We have 4 of those gladware divided plastic dishes and I've packed 4 salads and sandwiches in for lunches out.
Had the same bag on top a normal rack on a single trail a bike and had to make my own mounts for it. The seatpost clamp is a hanger for electrical conduit.