Why not go aluminum and use a silicone pad custom sized?
Go to Alibrother or Alirubber (two names of same business) or Keenovo. Their silicone rubber heaters that can be made one-off for reasonable cost. Keenovo makes nicer heaters but my Alirubber one has been working fine.
@Jeff_DeMaagd agreed. My Alirubber pad is excellent