Wow, didn't know this thread was still alive until I was doing some additional searching a few minutes ago. I thought I might be able to give back with what I have learned so far.
A double DIN radio will fit, but leaves a gap on both the right and left side. After doing a lot of image searches, I took a gamble and assumed a 2013 Frontier has the same radio (which also seemed to be confirmed after looking at wiring diagrams). I ordered the Metra 95-7619
http://www.amazon.com/Metra95-7619-Stereo-Installation-2013-Up-Frontier/dp/B00GNG3X7W
I was only able to use the middle insert and used a glue gun to attach it to the main dash kit.
The wire harnesses for the leaf are odd. You will need multiple harnesses if you want to maintain certain functions like backup camera, steering wheel controls, usb, etc to work.
Here is the completed harness in all its glory. I know it looks really bad, but I did clean it up a bit and tie it up nice. A bonus of the leaf is there is a lot of room behind the radio.
Here are the various connectors I used:
- Ax-nisusb-2 - for USB connector
- 70-552 - standard harness. I actually used the Scosche version and moved over a couple of additional wires for steering wheel controls from this harness. You could also just use 2 of these
- Ax-NIS32swc - for backup camera (more on this below)
For the backup Camera I used the Ax-NIS32swc harness. This harness says it is for steering wheel control, but I found it mostly useless for anything but the camera. The camera on the Nissan's (and some other OEMs) are 6v cameras. While I read reports that you could feed it 12v, I didn't want to risk it so I dropped in a 12v to 6v step down converter.
http://smile.amazon.com/dp/B00NICVEE8/ref=sr_ph?ie=UTF8&qid=1452869678&sr=1&keywords=12v+to+6v
I wired that into the harness and plugged the RCA into the back on my new double din.
The generic Nissan harness does not have wires for the steering wheel controls. I used a wiring schematic to figure out the pins I needed to use and then added wires from an extra harness I bought. If you get some good pliers, you can pull the wire out of the harness fairly easily and push it into the harness you are planning on using. I used the Axxess ASWC-1. If you look on their site for instructions for the Nissan Frontier, you will find the right pins and connections.
For me, I had so many different things to power, I used a relay to help distribute the power. You need power for the antenna, camera, steering wheel control module, emergency brake by-pass, the stereo itself and for a relay to any amps you are running. It seemed crazy that all of these things would need power, but it worked out in the end.
I am REALLY happy I made the change. It was a pain, and took a lot of planning, research, etc, but I love having a solid output to the amps, HD radio, Bigger backup camera, etc. I have only gotten volume controls to work from the steering wheel controls, but that was the main thing I wanted to work. I haven't had time to mess with it, but I wouldn't be surprised if it was something I did wrong that is causing the Source switch to not work.
Here is a (Bad) picture of what the rear view camera looks like on the screen.
Here is a first pass at the dash kit around the stereo. I ended up moving it back a little so it is more flush with the sides. *One note: Because of how far back the stereo sits and this particular stereo having a flip down screen, it doesn't flip down. I thought about spacing it out so the front of the stereo sticks out more but I haven't needed the CD/DVD slot in 6 months so I am not sure if it worth the effort.
If you have any questions, please let me know.