Yes David the plastic pieces do have barbs. I used EPMD foam from NAPA and from autozone. The stuff used between bed caps on pick up trucks and the body. 
It stuck into the metal parts and then I put the plastic
bits back on. I don't know if I would use the craft store foam 
as it doesn't hold up to the elements very well. 

Bill M
Mystic,CT

On Dec 10, 2012, at 4:41 PM, David Beierl <dbeierl@ATTGLOBAL.NET> wrote:

> At 01:21 PM 12/10/2012, Mike South wrote:
>> (c) remove the plastic, put my foam in, stick the plastic back on?
> 
> Yes.  Unless I misremember the plastic is held on by little barbs.
> 
> Yrs,
> d