It appears our esteemed colleagues have failed to address your concerns. First, I understand completely that what you are looking for is a built-in, Dash installed GPS display receiver, capable of APRS operations. This is a question of form before function, and a cobbled together system of outdated GPS receivers and radios stuck to your dash with glue, duct tape, and/or vent mounts is not desirable.
Secondly, from my research, none of the standard installable navigation systems include the NMEA communications protocols allowing you to have the unit perform as a nav/APRS system. This is frustrating. They have 90% of what we need, and if we had a talented hacker to solve this for us, we would be happy pandas indeed!
There are two options that I can suggest. The first is a "mobile computer" This takes a Double DIN car stereo slot in your dash and allows a special, SVGA touch screen monitor to be used with a "mobile computer" . These look a lot like mobile amplifiers, and are real computers that run on 12 volts and are designed for cars. They can be mounted under dash or under seat, and have all the regular ports, so you can run it as a Nav system with off-the shelf software, or as a NAV/APRS system with APRS software. You can find these on E-Bay, and besides handling Nav, they can of course act as MP3 players, FM radios, and have 3g and bluetooth connectivity. This is not turn-key or cheap, but beautiful and does not make you car look like something a crazy person drives. You will still of course need a GPS, but all you need is a cheap USB hockey puck receiver, like the type that comes with the mapping software from a variety of vendors, including Microsoft.
My personal preference is to build a Bezel to hold my Avmap G6 ( which is the only brand GPS receiver that actually supports APRS natively) and install it in the dash where the "junk drawer" goes. This hides it a bit, so no one breaks into the car to steal your GPS. Used with either a Kenwood APRS radio or Byonics TT4 and any radio, the unit does APRS as it was intended, and allows messaging, wiping off stagnant stations, and shows actual Icons instead of a dot and a call sign.
73,
Allen AF6OF
VHS/Byonics