After 45 minutes of screwing around (with screws, of course!), I got the handcart assembled. I disliked spending so much time putting it together, but that is the price I pay for the ability to transport the cart in my roof box. The black straps attach to a waist harness I made for pulling the cart. It didn't work (explained in another photo).
Ralph Tripod, who held my camera for this photo, is always fully assembled.