The Roadmaster Crossbar-Style Base Plate Kit # 3151-1A referenced in your question, which is confirmed to fit your 2014 Chevy Captiva Sport, does not include a mounting bracket for a 6-Way connector. For this I recommend adding the Roadmaster Electrical Socket Bracket # RM-910030-5 which just needs a flat surface on the vehicle on which to mount.
I have attached a short video review on the bracket that you can check out as well. view full answer...
You are correct. The only thing that comes with the Draw-Tite Max-Frame Trailer Hitch Receiver # 75556 is the trailer hitch itself and the hardware needed for installation on your 2015 Chevrolet Captiva Sport.
For a trailer wiring kit I recommend the Curt T-Connector # C56257. This plugs into the wiring behind your tail lights and just needs the wire run to the battery to power the trailer lights. This gives you a 4-Way flat connector for basic trailer lighting functions.
To complete... view full answer...