After doing some more research I see that some places do coat the inside and outside.

That's a good thought Pierre that the metal cools more slowly when coated on both sides. It would take longer to heat up and longer to cool down. Makes sense to me.

I found a company that sells a ceramic type coating that you apply with a paint brush, but they couldn't tell me anything about the heat transfer properties.

Anyone know of a place in Ontario that does ceramic coating?