Well, it appears, I'm late to the party. You've already made your cuts. I was going to mention that I would have suggested placing your fans on the ends of the amps, not on the sides of each one. The way you have them now, you are only efficiently cooling one side of the heat sink. The other will be practically a back eddy, where heat would stack up. With most amps, you don't need a gale force wind to cool them, just air to circulate around them.
So, you could have made air dams on one END of the amps, and had the fans **** the air out. Vent hole on the face of the left side of the 2x10, to let air in, and a vent hole on the right side of the face of the 2x10, for exhaust. This would farce air to travel along the heat sink fins, and vent out the other side. As well, you would not have reduced utility of your cargo area, as you now do. ~ i.e.- If you place anything like groceries or luggage, in the rear area, you will block your vents.
Sorry, I was late to reply.