One of the hurdles I've had is to devise a well-engineered lighting system that can be universal across anythign I might build, to work with any tractor. I'm not sure I have 100% compatibility yet, but I think I have something with potential to reconfigure as needed. As an example - this trailer has separate stop and turn lights, and also backing lights. Not sure I'll be doing backing lights on any future trailers. I can predict doing a separate marker light circuit, and with S/T on a separate common LED.
I dislike the bulky connectors that Tamiya uses, and I found some USB-C stuff I like better. As with most things, it's really easy in the mind, reality is a bit tougher. The USB board had to be located correctly to fit it in a narrow band between the bottom edge of the bulkhead and beneath the floor slats. And I still had to shim it due to my errors. But I got the slot CNC'd perfectly on the first try, so that's something. All of the wiring is 22 or 24 ga from a spool for RGB LED light strips, with 2 extra solid-conductor wires from another spool I scored somewhere.
The 2 white blocks are cross-drilling to hold the bulkhead and trailer bedplate together.
Looking back, I wish I had done lightning connectors instead. But realistically, it won't get plugged/unplugged all that often.