An android tablet ia a logical choice for a car PC. The device offers additional features beyond regular car stereos. While many car stereos have GPS, the android device offers a more intelligent GPS. It has all of your google contacts addresses already in the GPS, it has your calendar with events and their locations, Chrome to phone can automatically send directions from your computer to your car. The device can store music, use internet radio, or play music using a cloud player such as Amazon cloud. These are features not available on even the most high end luxury cars.
I recommend choosing a tablet that already has a car dock. This dock can be easily modified to be permanently installed where a double din CD player would normally go. Also, with a car dock, the device will be easily removable so you can prevent theft and use the tablet elsewhere.
Soldering Iron (Recommended)
Dremel with Cutting Blades
Tablet with Car Dock ( I chose Samsung Galaxy Tab 7+)
1/4" Sheet Lexan (Approx 10"x6")
1-1/4" Hole Saw
3/8" Drill Bit
Car Audio Adapter
Wire - Heavy Gauge to Power Amp
Wire - Medium Gauge for Speaker Signals
Step 1: The Audio
Replacing the stock stereo unit with a android tablet requires an external amplifier for the sound to play through the speakers. I choose a 4 channel amplifier. Four channel because my car has four speakers. I have the amplifier mounted under my passengers side seat, but the amp could be mounted just about anywhere. I chose just about the cheapest amp I could find. I don't listen to much music, mostly audio books and podcasts, so I was not too concerned with sound quality. I do listen to music using this amp and it sounds good enough for my ears.