BLIS requires two radar sensors, brackets and associated wiring behind the bumper. They're essentially standalone units so it can be done. In a 2018 you should have door modules so you'd wire the BLIS modules to power, ground and network, and then they alert the IPC over the network. You'd need forscan or similar to correct the as-built as I believe BLIS modules have the VIN coded in them, and you'd need to enable cross traffic in the IPC (and maybe BCM as well can't remember what all modules it routes through). To have blind spot alerts you'd need either BLIS mirrors and harnesses or you can manually wire an LED in on either side to a couple pins on the door modules, IIRC they're just a 12v trigger that lights the LED in the mirror.
