94 audio?

as you guys and girls know the rodeo/passports have 4 4" speakers and its not a good sound at all, just so open. Im not real into bass and stuff, but I do miss having a full sound in my car (my mr2 sounds great and its all OEM stuff).
any options?
i want to keep it clean as far as the install, id like to use stock positions, anyway to squeeze something bigger than 4" in there? what about the rear? any custom mounting points?

just looking for any advice other than "add a sub box" or something like that, I dont want something that'll take up much room as I often sleep in the back of it when going to races

My solution takes up a little room but not as much as a sub box. I just got some cheap flat pack 6x9 speaker boxes from walmart and added 6x9's to the back of mine. I know the setup is different between 1st gen and 2nd gen. In the 2nd gens the front speakers are 6" in the doors but have 4" speakers in back. These add much needed bass without taking up alot of room. And I didnt mount them to anything so I can move them out of the way when needed. They just sit there and never move, but you could use some velcro to hold them to the carpet.

http://i30.photobucket.com/albums/c337/Gizmo420/Img_0333.jpg

thats not bad, ill look into that, i just want to make it louder/fuller sound and not take up much space if any at all