My cork-like-asphalt-liner-underlayment thingamagig(I think that is what the
Bentley manual calls it:) was also falling apart.  At this point I am not
sure what I am going to replace it with.  I was considering something like
coolpatch or that brown bread sound deadening stuff with a layer or two of
felt carpet pad on top.  
My problem is the rust.  The use of POR 15(?) has been suggested several
times but it is pretty toxic stuff.  I am also not sure if it is a rust
remover or rust converter.
Anyway there are my thoughts.
Coop