Rather not spend a ton of money on metal U-channels? I made a printable U-channel which I've used for a few months on my MK3S+ with no issues. The light is very bright, so you may want to add a light diffuser, but I've found the extra light to be helpful.
Due to length restrictions, the U-channel consists of four pieces (for a dual light setup); two per side, with a connector in the middle to connect the two pieces.
I'd recommend gluing the U-channel into the bracket end, attaching both brackets and then gluing the connector when in-place. Then attach LEDs and wire it up!
The author remixed this model.