if you want to save space and not have a box in the hatch i would say you could build a fibreglass encloser to replace the factory 8in sub box , for the time it would take to make it nice and factory looking it really is just easier to get the jl audio stealth box. it comes with a 10w3v3 2ohm 10in sub already mounted. just pull the side panel,remove plastic oem box , bolt in jl box and remove the factory carpet section from interior panel (very easy). basically run your speaker wire to box and put things back together.all in all very straight forward install. I myself like jl subs and have used many over the years without any complaints. i actually have a 8 and a 10 from the w3v3 line sitting around the basement until i can find a place to use them, only one car so they will have to wait their turn..lol.
amp wise i am running a jl jx500/1d ...500 with a rbc-1 remote level control mounted inside the factory switch bezel under hvac for some bit of factory look (removed the control (?varistor?) from jl knob holder and it just fits inside of unused switch spot). to feed signal to amp i picked up a pac c2a-chy23 i think. It has front and rear outputs (rca) which are volume controled but are before bass or treble adjustments and are unafected by raising or lowering deck bass so i set what i think the factory speakers can handle bass wise and the turn up the level on the sub amp to rumble. the pac also has a remote turn on output to turn on the amp. im sure the signal sense turn on is fine but since it had an output i used it.
there is alot of reasonable space in this thing to stick an amp...under back seat (seat down size limiting), under drivers seat,under cargo floor,behind drivers side cargo panel(never checked room over there so dont know what size, addition of vents would probably be a good thing,factory amp back there down low).
over all it is much better than factory,would i like more boom,sometimes ,but this will do. ps. for more stealthy look i also blacked out the jl logo on sub and placed a ring of black carpet over sub mounting screws ring so it disappears even better.