This is AWESOME, thanks!
Some thoughts that might help:
First, the Side Object Detection (SOD) modules are generic and are used on several different vehicles. Special attaching brackets are needed that are specific to our trucks. These are bolted to the vehicle with three bolts.
If you're adding this to a truck that doesn't have BLIS, you'll need to get at least one used module from a 2015-17 Expedition Platinum (the only trim level where BLIS is standard). The reason is you need the configuration information stored inside the module in order for it to be usable. You can get a brand new module, but it will be "blank" and will need to be properly configured before it will work properly. If I'm not mistaken, this can be done with FORscan. Be sure to download and keep a copy of the settings inside the used module. From what I've read, the VIN number will need to be written to this module. There may also be other critical info that helps it function correctly for our trucks (vs being used in another vehicle).
Ford changed the part number for '17 models and there was a huge price hike. The older units were less than $200 brand new but then they suddenly jumped to about $600 each. The older units had part number
DG1T-14C689-EA but for '17 it's listed as
DG1Z-14C689-B. The number listed on the module is referred to as an "engineering number" and often won't match the number used by the Ford parts guys when ordering. I confirmed the
DG1Z and
DG1T numbers are actually the same module. So, if you're buying new, it may not be necessary to get the more expensive
DG1Z module from Ford.
Second, while I haven't seen anyone attempt this on an Expedition, I did follow some threads on an F150 forum where it was successfully done. Over on that board, I notice a lot of people buy entire wire harnesses just to add a module. This can add a huge amount of work and a good deal of extra cost.
In the case of BLIS, the connections are spliced into the existing harness. They are not part of a separate "sub" harness. Thus, you'd need to replace the entire rear harness of the truck! The cost for a brand new harness from Ford would be prohibitive. Because it's a lot of labor to remove them, many salvage yards won't sell entire harnesses. Also, the main harness is different for EL vs standard wheelbase. And, to make things even more difficult, BLIS was standard only on Platinum models. It was a rare option on other trucks. Thus, you might have a difficult time finding the harness you need.
For this project, all you really need is a connector for each module. This has power, ground, two wires to splice into the vehicle network, and one wire to run back to each mirror. Connections for +12V, ground, and network are located in the back of the truck already. So, in my opinion, it makes more sense to get the pigtails and run the wires yourself.
If you do this, be sure to get connectors for the RH module. There is an extra pin in this connector that's connected to ground. This tells the module it's installed on the passenger side as opposed to the driver's side. If you get the wrong connector, you'd need to find and add the appropriate pin. On the other hand, if you had two RH connectors you could simply cut the extra ground wire and use one of them for the driver's side module.
The harness will need to be secured to the structure near the module. The wires then run through the large grommet at each tail lamp and into the vehicle.
Shown below is the entire rear harness for a 2017 EL Platinum:
It should be doable as it's been done before with F150s and the setup is almost identical. I don't think adding the hardware will be a problem. More likely, it will be getting FORScan to work making changes in the code in whatever modules need modifying to get it active and working. 
