Thanks kamold,

My camera is going to be a replacement hatch handle, between the 2 licence plate lights, not the VW badge type.
I'm likely to run 5 audio cables to the boot space as well, initially just for the sub, but if required to replace the head unit amps.
I already have a down firing box sub and 5ch amp from previous car.

I've checked the 12 volt socket in boot space; that turns off with ignition so could use that to turn camera and amp on/off if required.
obviously need to run some heavy power cable for amp itself
Dont recall seeing a trigger output from head unit though.
maybe the amp will audio sense.... Must check.
And the reverse lights should trigger the camera.
There must also be the OEM power cable for the boot release as well if needed.

So I think I will be removing trim.

Thanks once again.