Have someone help you lift it into place and see how tight it is. If you have a half-inch gap on either side, you can call yourself a genius. If it's grinding as it's going in and out, it's going to bug the crap out of you every time you move the pan. Furthermore, as everything fills with sap and heats up, it could get even tighter. If it's too snug or even too tight to get the pan in, just remove the bricks. You don't need them back there anyway especially since you put insulation in. If you are not in a hurry, you could put half bricks in or even another layer of the ceramic board.