Hi tdub. My first install took at least 3 hours (had to figure out some things that were unclear), while the second took 2 hours max... It is not that hard but if you're not used (or willing to) do this kind of stuff then I really suggest you hire a pro.
You have to install it behind the RNS850 because you've got to connect the cable that goes behind the cd player on the carplay box, and then back to the cd player... And the cables aren't that long. I installed the android module (the one that connects to the iphone) behind the RNS850, and I had to put the other box (video box) in the space between the glove box and the RNS850 because of cable length limitation.
You have to tap 3 wires from the car and to provide current to the unit. I used posi-taps and highly recommend them. Very easy to work with. 2 wires (can+ and can-) have to be tapped behind the thermostat control module (this is relatively easy). These 2 wires will make the LCD automatically swicth to camera view when you put the car in reverse (and switch back on carplay afterward). The other wire you have to tap is behind the CD player (MMI wire in order to switch to carplay when you hit the NAV button). This is much harder because you have to remove the glovebox. I highly suggest you don't undo the big connector behind cd unit because I was not able to put it back completely on my first install (2012 Treg). For the second install I did it quite easily with the connector plugged in (just take the time to locate the right wire - and this was clear in the instruction).
The most scary operation was disconnecting the LCD screen from the RNS850 and pass it through a small board using film connectors... I was scared, but it's actually very easy!
I also passed the microphone cable behind the dash and put it right in front of me near the gauges (now siri works as well as phone calls). Very easy to.
The system connects to the auxiliary input of the car through a 1/8 jack (they provide the vw mdi adapter and everything). So the car needs to be in media, aux in order for the sound to go through the car audio. Also I deleted my iphone from the bluetooth otherwise the phone was ringing at 2 places at the same time (rns850 + carplay). The only problem is if you're listening to the radio, then you will not hear the phone ring in the speakers (remember you have to be in media-aux mode)
Also naviplus were very helpful and answered quickly to my questions.
Once it's installed. It works pretty much flawlessly... I experienced some disconnections but I heard that carplay is very sensitive to that. It could be related to the state of my lighting port. Needs some cleaning.
I'll post pictures but I did not take any while doing it. Sorry.
