Pictures were before it was completed. I added a frame member to that joint, 1/2" by 3" x 24" CR flat on the underside (on edge), tying the A to the outer tube frame that mounts the axles... so is more than only the butt joint.
I had added that part and a couple of cross members tacked in and went away on business. A friend that saw it under construction bought it while I was gone (it was not for sale but he needed it). He stressed that he would complete the weld out...which he did. He bought it to haul firewood out of his woods, finished welding it out and never once has complained of it failing.