I'd see if you can find a factory monsoon sub box and use that. if not then I'd make my box in similar shape and install it where the monsoon box goes. There's no need to cut any of the rear deck out and I would not advise it.
You can wire whatever you want but if you wire them all up parallel then you will reduce the ohms to probably lower than what your amp can handle and it will run hot and burn up. the factory sub was a dual 2Ω voice coil. also, what are you using for the turn on wire? it's possible your amp could be on all the time.
You can wire whatever you want but if you wire them all up parallel then you will reduce the ohms to probably lower than what your amp can handle and it will run hot and burn up. the factory sub was a dual 2Ω voice coil. also, what are you using for the turn on wire? it's possible your amp could be on all the time.