Using lead to fill trim holes


'Back in the day' before the hazards of working with asbestos were known, I used to use a product made from it that was in a wet paste form. You'd apply it to the areas around where you were using a lot of heat so it would absorb the heat like a heat sink. It did help prevent distortion. I don't know if a safe alternative is sold these days.

Eastwood makes a product that you wet and stick around the area your heating, never used it but probably going to give it a try.