Not sure if there is value in copying it, but the Seattle area buses look like this:
It's basically a permenantly attached trailer on the back of a bus, so there are three total axles and it articulates in the middle. The front and rear are connected with an accordian-like material.
I've thought about building a triangular shaped plywood box on the tongue of my travel trailer. My thought is that is would improve aerodynamics while towing, but also provide some storage space for trailer related items that I could get out of the cabinets in the trailer (it is somewhat light on storage space). There may not be a lot of gain economy-wise, but the dual-purpose nature would make up for that.
I've also put some thought into lowering the trailer, as it sits quite high. I think this was done to keep the fenders from intruding so much into the trailer, but the overall height are much higher than most of the other trailers I see at the campgrounds.