what you should worry about is the pain in the arse cutting holes in the rear deck might be. check your rear deck; mine is a triplethick layer of steel. It would take me 10 hours and half a dozen air body saw blades to cut those holes.
you do have another opton, though. if you purchase new front speakers that have adequate low frequency extension to match up to the xplod in the trunk, you can try simply removing your rear speakers, and using existing holes to let all that nice bass into the cabin
But I would guess your rear deck will be way too thick to bother with. doublecheck of course, get back to us.