I mostly have just put deepots (the round ones) in 5 gal buckets or similar size pots. The racks that are made for them (the new model, not the old flimsy ones) are pretty nice, but definitely add to the cost of what are otherwise pretty affordable pots, so I just have one of those. You can see in this photo what I do with most of them for now:
I would worry that a bungee cord might slip to the bottom if you’re shifting things around at all, since they have a tapered shape. It would probably work better for the square treepots though.