I've been working on a similar project intended to provide vehicle location capability for rural transit systems- http://humblehackers.wikispaces.com/Rural+Transit+Vehicle+Tracking+Device
I can tell you what I've gathered so far...
I've been using a shield called the TRAlog
The shield combines a Sierra Wireless WISMO228 GSM-GPRS module, a Globalsat EB-3531 GPS module and an SD Card on one shield so its perfect for vehicle tracking applications. After an extended hiatus from working on this project, I picked it back up again after the manufacturers released a sample tracking sketch of their own-http://www.rocketscream.com/blog/2012/10/17/vehicle-tracking-logging-using-tralog-shield/
Nevertheless, the code still has some bugs to work out and I have been in contact with the developer to try to work them out. As far as I know there is no public thread dedicated to TRAlog development but I would be willing to contact the developer to start one if you are interested in participating. The Github page can be found at https://github.com/rocketscream/TraLog
As for the web tracking, the TRAlog sketch uses the Web service at www.cosm.com
to track the positions ( see the feed here-https://cosm.com/feeds/72776
From the Rocketscream blog post-
We created a Cosm feed here which has a latitude and longitude data stream. Without graphical geo location mapping, it would be very hard to visualize the movement of the system. Cosm provides a simple geo-location mapping utility called Trails that can be placed on any regular website. However we found several limitations:
The data points selected from the feeds are spaced out and hence produce jagged way points on the map.
Only the last 24 hours of data is mapped.
But, it gives us a rough idea on how everything would look. We are currently looking into writing a server side script that performs a HTTP GET request on the Cosm feeds and provides a geo-location mapping visualization using Google’s mapping API. This will be next in our to do list!http://www.rocketscream.com/blog/2012/10/17/vehicle-tracking-logging-using-tralog-shield/
Even though the code is meant for use on an Arduino Uno, the developer created the code on a Mega using the Hardware Serial port and I'm testing its use with the Arduino Due to take advantage of the 32bit processor.
One more note about the Web-based mapping. Have you considered using OpenStreetMap instead? It might be easier to work with initially and you can download a feed as a KML if you need to use it with Google Maps.