Behind Backseat
 

I have looked all over but how much airspace is behind the back seat in an 01 screw. also how deep is it.

Not much, what are you trying to fit back there?

Bout 1.2 cu ft maybe a little more or less depending on what thickness of mdf or if you use fiberglass. I measured it at about 5" of depth where subs would likely be mounted due to the slanted seat back and room for excursion