I found my tin at a second hand store. Beware - these things get hot enough to burn wood and bedding.*Just above it* --- so the bottom of the waterer did NOT touch the top of the cookie tin at all ??
Just to show that anything warm underneath is sufficient, I assume !
About cookie tins ...
For some idiotic reason, I was NOT capable of finding a cookie tin
anywhere in the house or at the neighbours !,
I even looked for something like a cookie tin at Walmart.
What I did find was those baking pans and thus made mine that way.