[AceX]

Its been done on alot of car stereo competition cars for a long time. Creates a really solid base and sound insulator, but most have strayed away from it for various reasons. A liberal application of dynamat will do the job just as well IMO and you won't have to worry about any expansion/contraction issues that may arise, if the floor ever starts to buckle or buldge, and of course, the mess of removing it if necessary.

Wood is much more dynamic than metal and the fewer differences in materials, the better. It eliminates potential problems later on.