http://www.dogcages.net/index.htmWhat an excellent idea. Fitted car cages are the safest way to travel as they protect your dogs from going through the windscreen in the event of a crash, prevent dogs escaping should the windows break/doors open in a shunt etc, enable you to keep the doors and windows open should you need to when parked in hot weather, and protect the interior of the car from being destroyed (not to mention snotty windows) :D
I drive an estate and my back seats are down and the whole car is fitted out with a double cage, (could fit 4 cages in but my dogs spend a lot of time in the car so they travel in 5 star luxury) made to measure by barnesbrook (see link above). Fabulous quality, rattle free and cheaper than a lot of makes. Complete with lead hooks and escape doors.
HTH