Why would you want to put it in the Dashboard as you wouldn't get such a good view. I put mine behind the rear-view mirror and hid the cable behind the headlining, windows plastic and under the dashboard - simple enough, only took 30 mins.
Mine has no rear view mirror so will look ugly. I do however have a phone holder mounted in the dash, I was thinking I could put a camera behind this. simpler cabling and as its raised it should give a good view too.