building a false bottom trunk floor.

I want to build a false bottom trunk floor so that I can make a amp rack in the floor of my trunk. What I was thinking was to cut out 2 pieces of plywood that are shaped like the trunk floor-board & then sandwich the amps in between the plywood, which would mean the floor on the trunk is raised. This is an advantage because I can keep my spare tire, but my trunk space will suffer greatly.

Which is better making a raised floor or making a rack below the trunk floor level? If I make a rack under the trunk level, I will have to remove my spare tire. How are these things usually made & what kind of wood is usually used? I do not want to weigh my car down too much.