I am getting rid of my other 75 lb bulky box out of my trunk and going with somethin lighter. I an making the trunk flush and i want to put a sub in the middle where the spare goes but theres not that much room so it is either a shallow mount sub or a reverse mount... What are the pos and Neg on reverse mount? How much air space are usually need for those? and dont you have to hook those up backwards to hit backwards? im a newb when comes to this. Thanks