Door Schematics?

I have a 95 Isuzu Rodeo S, and it only has spaces for two speakers up front. When I installed the my system I discovered that they already had 90 Watt 2-way Kenwoods in them so I didn't switch them to the 75 Watt 2-way JBL's I bought. Although these speakers are fine mids with the bass blockers, I feel like there is something a missing when i listen to the system. I basically have 2 front mids and one 350 Watt RMS 10" Sub in the back. I want to add more speakers but I didn't see any spaces for any more. I figure I'll have to cut the door's plastic panels at the bottom but want to know the shematics and measurements of the doors. Does anyone know where I might find this information or should I just crack open the thing and figure it out? *mind you I've never taken apart a car door.