plan to mount an amp 400 . Using plywood, I would attach the wood to the back of the rear seat. I would mount the amp to it.

Sorry for the confusion Nick, but it sounded like you were going to mount the amp on the inside of the passenger cabin, somewhere behind the rear seat, either on the backrest or under the seat cushion. If the plywood panel is going into the trunk, then there's really no concen about overheating, there's plenty of air in the trunk to dissapate the heat from the amp's heat sink. As for positioning subs, there are several options. Subs in a proper enclosure can be mounted in the trunk, either towards the passegner compartment area, or built into corners where the trunk pockets are. Porting the bass into the cabin can either be done by removing the first aid kit plastic box and creating a grill or by removing the rear OEM speakers and using those openings as ports. There are also smaller free air subs that might fit onto the hatrack panel without a rear enclosure, and standalone powered subs like the Infinity.