Hi;
I used self adhesive roofing membrane with a foil back in 5" or 6"
rolls.  Was 20% the cost of the commercial sound deadening products and
has virtually the same thickness.  Don't look for huge improvements but
the doors and hatch do not have the tinny sound when closed.
Your should be able to find a similar product at Home Depot or another
building supply dealer.
Here is one link

http://www.resisto.ca/

Wade Yorke
Truro
Nova Scotia
'84 Westy 1.9TD

Wade Yorke
Truro
Nova Scotia
'84 Westy 1.9TD