The durability issue has been argued extensively. Having followed and participated in the argument for 6 years, I can tell you that a very common progression is: 1) strongly endorsing the durability of asphalt based products. 2) having the asphalt melt out. This has occurred with several well known advocates of extremely precise installation techniques. This isn't to say your P&S will melt. The VOC's could have dissipated enough to leave the asphalt as a hard and relatively stable crud. It is to say that there is a high failure rate. 66' X 3' for $200 works out to a buck per ft². Now consider that the marketing hype I'm pushing suggests covering 25% of the surface with a proper vibration damper. Compared to 1 layer at 100% coverage, you're paying the equivalent of $4/ft². 2 layers and you're $8/ft². That really kills the cost advantage. More material means more work. Add having to heat it and it's much more work. What happens if the material needs to be removed for body work? That's not to say that multiple layers of P&S won't create a barrier - a very light weight barrier, but a barrier none the less. It would actually work better if you didn't remove the release paper on the floor. So it's really a balance between doing more work for less performance. Throw in the durability "questions" and it just doesn't make sense to me.