PCB coating for a high temperature environment
There are silicone based conformal coatings, available as spray. They should bear this temperature range easily. Polyurethane based sprays may be used, too. We had tests running with PU. It proved usable up to 90°C. But all depends on the actual use. You can buy those materials manufactured by several companies like CRC industries, electrolube etc.

If you want to increase creep resistance by using a conformal coating, you will have to do several tests anyway.