[C320-list] Looking for putty

[Scott Westwood]

I need to fill an irregular concave void for a backing plate on the inside of rough fiberglass.  I heard of a putty type material (I think it was pink?) that you can cram into a void and it would harden.  I don't want anything that will flex.
I could use that tube of grey steel 2-part putty but in my experience it cures brittle.  That would likely crumble with vibrations over time???
The void is small.  Maybe 1 inch wide by about 4-5 inches long and about 1/2 inch think.  I can't smooth it out enough.  I need to fill the voids.
Any thoughts? 
Thanks,
Scott Westwood scottwestwood at bellsouth.net H (919)-362-8538    C (919)-618-7185