In comparison to the truck proper, the trailer was pretty straight forward. There's not a ton of information on the web about them, and there's some variation, either due to multiple manufacturers or multiple contracts. In the end I opted to make something that basically looked like the 1:1, and would also work with the PLS and my existing racks.
The CAD layout looks like
same aluminum C channel frame and 3D printed crossmembers as the truck. The leaf springs are actually 3D printed as one piece, but if you don't look closely pass muster.
Axles are just M4 threaded road; the wheels then have brass tubes of ~4mm ID to act as bushings to spin freely on the axles.
a little snap on cap for the hubs
and they're a close match for the 1:1
The tired tread isn't quite right, but I couldn't find a closer match in the right size.
There's still a few tricky bits to this design. One is the front axle, which is mounted on a turntable (again with the skateboard bearings, cheap/widely available) so that it steers somewhat. However. for load/unload operations, it has to lock, so there's a hole for a brass tube to do so.
Further, to load and unload, the trailer has to be tucked very close to the truck's rear bumper, or the truck's arm can't reach. However, at that position, the trailer can only turn a few degrees before hitting the rear bumper. The trailer's drawbar must therefore telescope to allow two different positions (again, latched by brass rod from the LHS.) The 1:1 actually works the same for the same reasons.
This is the drawbar extended, but right about center of the pic you can see the second hole to latch it in closer. Yes, those are safety chains, and yes, they work. I discovered this when testing the trailer out in the driveway and something came unglued, and the chains kept pulling the trailer, just like they would on a 1:1
