No one told him that opening up the trunk more into the cabin wouldn't help him, of course it would. But cutting out the metal behind the seats isn't going to help a ton if the seats are still going to be in place anyway. His seats don't fold down stock, so he has to keep them in place for Street classes. You start cutting out a whole bunch of metal and A) It's permanant structural damage to the car, B) They could very well bump him up classes, to like SS where he would get dominated by the 160+ people.
For his car, I think it is just best to do the best that we can for Street C type classes. This is his DD, so he'll still have backseats and if he ever needs to sell the car, he'll be able to.
I'm pretty sure he doesn't have the height to fire the sub any way but up. I was thinking about doing sub up port side, trying left first and cutting the volume in half.