I've been towing my 2013 C-Max behind a motorhome for 4years, about 20K miles. I'm using a Roadmaster Falcon 2 tow bar, and Invisibrake braking system. The tow bar stays on the MH, and I remove the car's connections whenever I disconnect the car from the rig, to avoid having the car's proximity sensors from constantly alarming; the Invisibrake fits in the storage compartment at the feet of the left rear passenger (essentially under the driver's seat). It is a permanent installation, but the compartment cover still fits over it as designed. The only thing that was installed under the hood is a fuse/breaker box; it caused a lot of confusion at the Ford dealership-they were looking in all their databases to try to figure it out. Then they asked me...
The installer put a rocker switch on the dashboard to supply power to the braking system.
No real problems so far, but a few things to watch for:
I was told (on an RV Forum site) that you need an extra wire from the MH to the car to provide 12 volt charging to the car's battery (the brake system is powered by the car's electrical system, and on a 6-hour drive the battery can be drained). But when I had the brake system installed, the technician just said to turn on the MH headlights whenever you tow, and that will provide a charge to the car. So far it has worked fine, providing I remember to do it! I guess the take-away is to talk with the tech about it, to prevent dead batteries. I also carry an emergency jump starter just in case...
I'm sure you've been told NEVER to try to back up while towing. I used to think it was because of the potential of a jack-knife situation, and lack of visibility, but a Ford tech told me that it can seriously damage the transmission(s) on the car. Word to the wise.
That's about it. Let me know if you have questions.