After what I thought was much judicious research, I found an off-the shelf product to use in sealing my firewall; 3M FB136.
Unfortunately, while working on my baggage door, I discovered that it has cured rock-hard, has cracked, lost its integrity and has leached a white powder.
The label says its for "sealing interior construction voids around wires, pipes, HVAC ducts and vents, in wood or steel framed non-rated construction
." I figured the interior
restriction was not a problem, as it wasn't going to be exposed to the weather where I was using it. The label also says Store at temperatures above 32 degrees F
. Again, not a problem as far as storage is concerned.
I applied this to my plane last fall, and since then it has been as cold as 5 degrees F this past winter, and this is the result.
I'm now chipping it away, and would love to hear some successful stories about what you used.