C. I used thin sheets of closed cell foam from U-Haul dish pack boxes. About 1/16" thick; it's lasted for years. 

Karl Wolz
Sent from my electronic umbilicus

On Dec 10, 2012, at 11:21 AM, Mike South <msouth@GMAIL.COM> wrote:

> It looks to me like the heater flaps are constructed with a metal base into
> which a plastic rectangle was pressed, the foam seal being held between the
> plastic and the metal (don't know if the foam was stuck to the plastic or
> just held in place by it).  Should I
> 
> (a) leave the plastic there, and stick my foam to the plastic?
> 
> (b) remove the plastic and stick my foam to the metal?
> 
> (c) remove the plastic, put my foam in, stick the plastic back on?
> 
> mike