30hrs sounded crazy high to me too, maybe he just didn't want to do it.Best bass you will ever experience. That’s the payoff. And people who think ib doesn’t get loud are crazy. The subs will play high as well. Not sure about that one.
inwould do a baffle begins the rear seat and just seal up the rear deck. Don’t worry about there trunk being sealed.
Time to do it depends on ability and equipment on hand. 30 hours is stupid crazy long time. I did my first one when I was 16 with 2 pieces of crap plywood and a skill saw and a jig saw. It was 2 kicker 15 free air.
also, the bm is not a sub I would use for ib.
I talked to nick @ si last week about it. He said they'd work great ib so no worries!