I wanted some speakers 'cause im gonna blow the ones i have soon(not on purpose) and i was thinking was replacing the ones i had w better ones but heres my question. do u think i could replace my back seats with speakers. i have an '02 extended cab so those spaces seem like a good place for speakers

No problem at all. I've seen many done this way and it seems like the perfect spot!

you already have 4-6'x9' speakers in your truck. you could just replace these with quality ones and keep your seats and rear space. thats all i did to my 2000 supercab and it will vibrate the mirror loose.as loud as you can handle!!!

I had a 02 extended cab myself and the stock speakers were 5"x7" i replaced with boston acoustics and used the rear space for a small box with one ten and my ranger ROCKED