Installed today
I installed the eTrailer kit in my LTZ this afternoon. Took about an hour.
To clarify the instructions, remove the center threshold piece first before loosening the sides. Four pins pop up from the plugs, then pull the plugs out, then pull upward toward the roof to remove the threshold piece.
The sides are a bit difficult, but are doable. I got the upholstery and trim tools and it popped off easily, but I had to use pliers to get the green clip pins out of the body before installing them back in place on the side panels. The left/driver's side is easier to get to the harness, which also has lots of room to place the control module, BTW.
I didn't take any pictures, as the instructions had pictures that were reasonably sufficient.
I hope that helps! I have to get a connector from the hardware store, and then I can test it all out once I connect it to power (at the fuse block).