Body Filler for Inner Fenders

So I did some rust repair on the inner fenders of my car. I butt welded in some new metal and ground it all down; it turned out pretty good, but not perfect. I want to skim coat it with something to smooth it all out, but since it will be near the exhaust, I want to make sure I use something that will hold up well to heat. I see All-metal, Lab-metal, and high temp. Lab-metal as some metal filled body fillers that seem like good candidates, but I don't have experience with any of them. Does anyone have any experience with these or something else that can handle under hood temperatures near exhaust headers? They are small areas, so I am not too concerned if its difficult to work with or sand.

Thanks for any and all input.

Edit: Picture added for clarity