Thank you shifty, I will consider it if what I am trying fails, but I am pretty far down this road now...

I am about to place my order for some elastomer tomorrow, I have been sending alot of emails and making alot of calls trying to find what product best suits me,

The idea so far is to use the Eratwowel MT80A mixed with some black pigment, for one side, and to use some high temp silicone mixed with black pigment on the exaust side, pack it with some fibreglass to stop heat transfer and back it with Eratrowel MT80A to keep it from deforming, as the Eratwowel has a much higher duro than the silicone.

I want to use high temp silicone on the exaust side as the Eratrowel is only good for around 90deg c.

I went to a company near work that makes bags from silicone and uses a weave in the centre for strength before work today.
From what I saw this morning silicone will do the job and look right.
I just have to see if the pigment I am ordering for the Eratrowel will work with the high temp silicone the guys near work are using.