My mom has that very exact car - well it is an SE (I don't know if the ST can be towed). And we have a 2014 Ford Taurus that I was going to tow, but when my mom bought her Focus, we bought her old car - a 2002 Pontiac Grand Am, which is also towable. I just could not see drilling holes in a new car.
I have bought the baseplate for the Pontiac, which came in on Monday, but the car is in the shop getting the transmission serviced along with brakes, etc. to bring it up to par so it can be towed.
After I get the car back from service, I'll start installing the baseplate.
Some of the research I did revealed that different towbars are easier to install than others, so you might want to determine which one to use.
I went with the Blue Ox baseplate as the Roadmaster baseplate required removing engine bolts and lifting the engine on my Pontiac... not something I want to do - or pay someone to do.
Here are the installation instructions for the Blue Ox baseplate:
If you go with the Roadmaster baseplate, I think Camping World still has their $16 installation deal going until the end of the year, so it might be a bit cheaper if you do not want to do the install yourself.
Generally - you have to buy the towbar and baseplate from the same manufacturer, but for some baseplates, there are conversion brackets that allow use of a competitor's towbar.
The only real concern I would have is that many current model Fords have a dynamic air shutter that needs to be taken off the vehicle for some baseplates. This may reduce the gas mileage slightly, but probably not by much.
Here is the install instructions for the Roadmaster baseplate:
The Blue Ox baseplate seems beefier to me, but the Roadmaster bracket seems simpler to install.
One odd thing though that I see for the Focus, you need to disconnect the battery. But for my Taurus, you don't need to do anything, just put it into ACC position (not ON like for the Focus). Wonder why vehicle manufacturers cannot have some consistency among their models (for example, the 2014 Fusion cannot even be towed, unless it is the electric or hybrid version).
Also, I think the Focus can use a "bulb" kit for the brake lights. For the vehicles that can use it, you basically drill a hole in the backside of the brake light bezel and mount a dedicated bulb that goes directly to the brake light connector from the RV.
This alleviates messing around with diodes and keeping the tail light systems independent.
I could not do this with my Taurus as the LED lights don't allow for mounting another light bulb as there is no room in the tail light bezel. But the Pontiac does have room, so that is how I am going to connect brake lights.