The best trunk mounted bike rack that fits your 2014 BMW 640i convertible that also happens to fit your budget is the Thule Passage part # TH910XT as it has an easy to install design loaded with great features like shock absorbing frame cradles, adjustable arms, and a wide arching design that fits vehicles easily.
If you plan on carrying any women's or alternative framed bikes without horizontal top tubes you may also be interested in purchasing a Kuat Bike Frame Adapter Bar # UB01 to... view full answer...
The # HM47200 would indeed adapt your existing 4 pole to a 7-way blade-style trailer connector. In that respect, it would work just fine.
However, I typically recommend going with the # 37185 instead, as the adapter also offers a 4-pole connector. If your trailer doesn't have or need trailer brakes or a need for a 12-v power supply, you'd simply plug the adapter into your existing 4-pole, and ground the white tire to the vehicle frame. This will provide you with lighting functions, and... view full answer...