We use ultra copper RTV on rutland gaskets for the BGE. It is rated to 600F continuous.
I haven't checked if it is food safe or not.
edit from here:
PRODUCT DESCRIPTION S.I.N.: 834-300
Permatex Ultra Copper is a single component, room
temperature vulcanizing gasketing compound designed to
provide reliable “formed-in-place” gaskets for mechanical
assemblies. This material cures on exposure to moisture in the
air to form a tough, flexible, silicone rubber gasket. The
product resists aging, weathering and thermal cycling without
hardening, shrinking or cracking. Permatex Ultra Copper is
the most advanced high performance, high temperature (up to
700°F intermittent) RTV gasket available.
PRODUCT BENEFITS
• High temperature resistance
• Sensor safe, non-corrosive
• Superior adhesion and flexibility
• Replaces most cut gaskets
• Improved oil resistance
• Can be used as a gasket maker or dressing
• Non-flammable, Non-toxic
• Low odor