So i finally found a sub that fits behind the rear seats of the 1998-2005 hilux dual cab
SOUNDSTREAM Stealth 13" Slimline Subwoofer and Box
fits very nicely, you only have to remove one of the child seat attachment things and it fits with out pressing on the rear of the seat.
the box is quite large so there is not much room there but i did fit my amp there as well.
the SOUNDSTREAM Stealth 13" Slimline Subwoofer and Box is quite a nice sub. not at good as a proper size sub but i was very happy with it and most of the difference comes from being behind the seat and it is still very loud and clear.