I agree that I should have gotten 15s but I had to keep the cut 12'' tall or shorter or else Mike would have had to cut through a hump on the back of the cab. But now I realize I might be able to fit 15s in there sometime down the road. The cut came out to be about 31'' x 12''.
I left this morning at 7:30 to go to Mike's (hour and a half drive) and just got back at 3:00. I'm about to eat something and then go to work in the garage.
One thing i always wondered about blowthroughs is, when you put the box up against the cab how do you seal it up real good? The back of the cab isn't flat....Or does the cut out go the whole width of the box?