If you are building a false wall anyway, you can just use 3lb (or more dense) fiber or mineral board. These are the standard materials used in all the commercial pannels anyway. Owns corning 703 is one brand, but you might be able to find something less expensive. I used stuff from Ottawa Fibre that I found locally. Call around to building/construction supply places to see what you can find. As long as its 3lb/cu.ft. or more dense you're good.
Also, try posting your questions on
this forum or
this one There are a couple of pros that hang out and give advice on both forums. They will help you keep it as simple as you want.
