Type of "bondo" for firewall

What kind of filler should I use for my firewall? I've been using Evercoat Rage in other places, but I wonder if the heat from the engine will be an issue under the hood???

 

Never heard of anyone having problems.
But there are a couple brands of filler that will handle higher temps,Lab Metal is one.
They use it under powder coating,so it will handle 450F.

 

Rage will be fine.