I about have all my Dynamat Xtreme down on the floor of the Firebird and would like to put the rubber underlayment down over top to help control the heat better.

When I looked up the parts, I notice the venders sell a rubber or tar paper underlayment for a 67-69 Firebird. Anyone know which would be better and what the difference is?

The paper back tar paper $15 more but I guess that don't always mean it better.