Interesting idea Peter - I'll stick with Plywood for strength/soundproofing.
Max - is the Dynamat waterproof? Jon's right, if I put it on the bottom of the plywood, it's exposed to my differential and the ground and must be waterproof.
Chris - not an issue for me, my car is a 1966 Plus 4. The plywood hooks under two metal brackets near the spare tire, and on the edge near the seats has two wood screws. that's it, very low tech! My new deck will have a hole for my cutoff switch key, and I'm mounting the switch beneath the plywood on a bracket of stainless steel - so that I can take off the plywood and not have to disconnect the switch.
-N
