Our Minicell kits are very popular for floor insulation. Minicell is pretty good for reducing noise and does not require furring. It can be used over sound deadening if desired. Some customers are using Thinsulate AU4002-5 under floors and best practice is to do some furring around the perimeter of the floor in that case.
Experience has shown that it is not necessary to apply additional sound deadening to floors when using Minicell or Thinsulate. The metal floor is not really an unsupported panel that is prone to resonance and normally has plenty of stuff on top of it (thereby constraining it) when the build is complete. An area rug or mat is great for comfort and to further reduce noise (if needed).
We just received our first shipment of 3M's new Engineered Damping Material which is roughly half the weight of other stick on mass loading materials. We believe Thinsulate SM600L on its own (in walls and roof) is sufficient for resonance control, noise absorption and thermal insulation but some folks want to take it further. Saving weight in a van is important and we believe this material serves that need very well.
All the best,
Hein
DIYvan
High NVH Performance sound deadening material. This 2.9 mm-thick material features an engineered stem web layer between two layers of adhesive.
diyvan.com