John,I have something that might be suitable - I used it in my Corolla with the empeg for a few years. It is about the size of a good sized hardback book. Will check the make & model tomorrow.

edit:
This is the amp, and going by my install thread it is ~8 years old...
edit2:
Manual http://www.nodevice.com/user_manual/pioneer/car_amplifier/gm-x364.html