Replying to Subs for Truck

I was wondering if any of you know anything about Subwoofer instalation in a Toyota Tacoma Access Cab. I dont want to take up any room in this truck, but as many of you know, under the folding back seats there is a tool kit box and a jack box. I am sure that I can find some other place for these Items, and I was wondering if anyone knows if it is at all possible to customize those boxes back there for some sort of sub, (maybe the new Pioneer sub that is only 3.5 inches deep)