Reviving this old thread to share this astonishing find:
A European-based company named Hinterher/Munich produces enclosed aluminum cargo bike trailers among other things. Their largest model is the Hbox 880 L which features a tandem-axle setup for "self-balancing." The trailer utilizes 16-inch wheels and Schwalbe Big Apple tires.
Sadly, there is no video footage of this trailer in action, at least none that I was able to find. I'm rather curious to know how that thing handles while cornering or while the wheels are on uneven ground. Also, can the Schwalbes even achieve a notable lifespan with the extra abuse they'd be taking from tire scrub? I'm not actually familiar with that brand as I've simply never used them before.