Forgive my ignorance...

What is the best material to use for under coating?

Is the Rhino pick up bed material good for under coating? I asked about the material and it seems that it is everything an undercoating material should be... It protects from rust. It does not crack due to flex or heat. It does not chip. You can apply as thick a coating as you want. You can choose color to match your body color. It is good sound dampener. It is seamless when applied (meaning: no space between body and lining).

Being all of the above, why don't people use rhino material for under coating (aside from price consideration of course)?