RE: Sound Deadening with Flashing Material
I used about three rolls of this stuf in my Westy.  I placed it on the
inside surfaces of the outside  of the doors, slider and back hatch. 
Then replaced the vapor barrier on all.  Made a big difference.  I
also went under the rear seat and into the closets, etc and anywhere
that sounded hollow when I knocked on it with my fist is placed some
of the material.  BTW, it does a poor job of adhering to porous or
rough surfaces like the inside of the closets and cupboards.
I to ask the same question, if I were to place it on the inside of the
doors just under the trim panel, how would I get the trim back on?