I stopped getting rustproofing on new vehicles a long time ago. The last vehicle I had with significant rust problems was a 1989 Aerostar when it was about 8 years old. I live in Ontario where a lot of road salt gets used in the winter and parked that vehicle in my garage. Subsequently, my vehicles (including one we had for 13 years) that have been left outside haven't experienced significant rust problems.
I likewise wouldn't go with any product that drills holes in the metal. Your MKC has extra sound insulation as well as audio components, wiring, etc. that might be damaged if anything was sprayed inside doors or body cavities. Some people I know get an oil spray under the vehicle every fall.