I would definitely NOT recommend inside the boot lid that if you want reliable operation and good clean pictures free of break-up or interference.
The hinges will not provide a good return path. Much better to take the 12V and its earth wire back to the body part of the boot via umbilical - it’s easy enough and with lots of options, no drilling or rubbing down.
Always, always keep the video lead intact all the way from camera to display, as MickAP did, or rf as I did.
Finally installed the reversing camera today, very pleased! Getting the wiring up to the front was a fiddle but I managed that no problem, also managed to get the wires nicely aligned through the grommets in the boot lid, so all neat and tidy. After a couple of rookie mistakes with the connections I got there in the end.
First I wired it to the fog lamp not realising the MX5 only has a reverse on the passenger side 
. Once I had the wiring at the back correct and the RCA connected to the head I could access the cam from the camera app on the unit but not automatically when selecting reverse - turned out I hadn’t actually connected the reverse sensor wire, so connected that and the handbrake sensor as well. But still nothing when selecting reverse 
.
Then I noticed that when the handbrake was on the camera came on. Turns out the reverse wire (purple) and handbrake wire (green) are the opposite colours to the corresponding wires on the control harness - so swapped them around and hey presto! Everything now works as intended.
You live and learn as they say and it’s all good experience!