Yes I know exactly what you mean!!! there's not much room behind there.
The best fitting one i've found (in a 93 model rangie) is an Eclipse cd7000. They're not cheap though; but awesome sound. My dad's a sound engineer and he said it's one of the best he's heard.
I've also found a kenwood 10 inch sub. with instructions included for suitable boxes. By chance this box will bolt in where the origional was, and sounds sooooo good!
On it is a 7 band eq, time alignment, inprinting, and heaps more.
It has 2 rca inputs, sub out, gps in and round plug cd changer in (theoretically it should run the origional cd changer, though I've not tried this yet) siruis, and hd radio. It'll play mp3 and wma off cd/r/rw etc. however not off dvd. It's bit old in terms of connections and stuff, but it sounds soo good.
hope this helps.