I've heard of using this stuff to seal the gaps on smokers and it's been suggested that it's ok to use the Ultra Copper on the smoker box as the temps don't get excessively high. Here's some info that was provided by Permatex on that subject,
..."Permatex has a High Temp. RED RTV Silicone Gasket Maker and is safe to use around food products .It is certified NSF/ANSI STANDARD 51 Food Equipment Materials ...( indirectly around food )Temp. max. is 600 F continuous and 650 F intermittently ... The Ultra Copper is not NSF..."
Thought this might be useful.