Depends on what you think cost effective is... One product used to
restore classic cars and used also in autosound competitions is
dynamat. Available at most serious autosound shops but probably
not in the very high temp form, which you can find at Eastman Co.
(they are on the web, check my links page in the lancia section -
I will add that to the links in the Peugeot section too). They also
sell the one for the firewall.
Ciao,
Francois Dion (francois@hyperreal.org)
-- Member: FLU #1722, PCNA http://www.fortunecity.com/silverstone/zagato/101/launch.html Alfa Romeo, Fiat, Lancia, Peugeot, Volvo, Solex