Does the attachment up high like that cause any handling issues? To me it looks like a load could try to toss you around a bit
I attached my game cart to the seat post using heim joints, then pinned one shaft for easy removal if the cart is needed for packing to and from the road. Basically heims allow it to move in almost any direction without jerking the bike around.
I haven't used it yet, just filled the cart with bags of sand to test. Works great in the driveway

Sorry I don't have a pic of it.