Sound deadning reviews

I am getting ready to POR 15 my floor in my '64 Barracuda. I am going to run a 2.5" exhaust, with 2 Dynomax Turbo mufflers, dumped before the rear axle. I want to lay down some sound deadening material and I have read a lot of the articles on this site about the different ways of doing it. I am looking for some long term results from the people who have put some in. Any thoughts/suggestions/issues that you have experienced is greatly appreciated, cause I only want to do this once! :profiler: