If you are mounting a camera at the back of your car then you're better off using a sticky type mount rather than a suction cup because, as you say, it might fall down when you slam the boot lid. You're probably going to access and use the rear dash camera less frequently, so relatively cheap but high quality cameras like the Aukey DR01 are a good choice. For wiring a rear dash camera you're best off getting it hard wired by an auto electrician, since they will route the potentially long wiring out of sight and set it up so the camera powers on with the ignition. Fortunately the service is quick, cheap and straightforward.