i was wondering if anyone with an extended cab has ever mad a custom box that would fit behind the fold away seats like the ones my 96 has if anyone ever did this post a picture so i get an idea of what to do

check the audio video tech section, there are alot of guys that made their own and did a great job. Also check the "how to" section interior tech

i checked and i couldnt find anyone that put them behind the seats

You would have to build custom boxes or buy them then. If you buy them check crutchfield.com for pre made boxes that fit behind seats. I had a set of JBL 12's behind my s-10 seats and they were great. Crutchfield is a company I have used for the past 15 years so I highly recommend then for your boxes.

alright thanks for the advice man ill make sure i check it out