Hi,
Appreciate that this response is rather late and you probably have resolved your dash cam issue. I am new to forum. However this may be useful to others.
I had a similar dilemma when wanting to add a dash cam to my S Type. I don't like trailing wires and I didn't want to keep removing the camera every time I park my car in case it gets stolen. The solution I settled with was a mirror cam. It has a 4.3" screen built into the mirror and the kit includes a rear camera. (see images below).
The front facing camera quality is very good and the rear camera quality is more than adequate. The camera uses a Micro SD card for storage. The things I really like about this cam is that the front camera is on the R/H side of the mirror cam (many are on the left and face away from the road in a R/H drive car) and the power, rear cam and GPS module (purchase separately) plug in to the top of the unit. This allows you to feed the cable/s along and around the headlining edge and drop down by the mirror post. I also fitted a dual DC to DC USB converter unit which I connected into the driver's foot well main fuse box. This does away with the need for dangling USB power leads plugged into the cigar lighter/AUX socket.
The camera stays fitted at all times as it is discreet and functions well as a mirror.
The only downside is that when the camera is active it "blocks" the signal from the key fob when locking or unlocking the car. I overcame this by not setting the camera to auto activate.
If anyone is interested in more detail I can provide some more images etc.
All items available on Ebay
Cam circa £40
Converter circa £5
SD Card circa £11