I have mine working. I had to reprint the parts with PETG filament to make them UV and sunlight resistant. The first ones warped.
I wired in a power switch as there are times I will use the system without the tailgate down (for example when camping and I have my hitch in). I also, just ran a standard amp wiring kit along the undercarriage rather than cutting into or modifying my 7pin connection. The 10 Gauge wire was much cheaper than buying the $90 pigtail.
BT Controller - https://www.amazon.com/gp/product/B00WVTS4R4/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
4" Marine Speakers - https://www.amazon.com/gp/product/B08P7CKXBD/ref=ppx_yo_dt_b_asin_title_o03_s01?ie=UTF8&psc=1
USB port - https://www.amazon.com/gp/product/B07SWZRFRS/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1
Wiring Harness and Wire - https://www.amazon.com/gp/product/B08FRRC4RN/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1, https://www.amazon.com/gp/product/B01C7O7Z68/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
Power Switch - https://www.amazon.com/gp/product/B07P68NFXZ/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
3d Printer STL Files (I printed them with PETG, and only did supports on the speaker mounts).
- Speaker mounts (these have a lip the slides under the tailgate metal, is is tightened down when you screw the speakers in https://www.tinkercad.com/things/cYdAZhWyiD6
- Blue Tooth Controller https://www.tinkercad.com/things/j6kqISHpcYt
- USB Port Panel - https://www.tinkercad.com/things/ldsRsnBkZs0
Here are the components I used