Specific ?? about cookie-tin water heaters:

[BridgeTea]

We're getting ready to make one of the cookie-tin water heaters, the one with the bulb inside the tin and a waterer on top.
About the waterer: I have a flat-bottomed stainless dog dish. I could put a gallon (rinsed-out) bleach jug inside that dish, with a hole punched in the jug at water level and the lid screwed on, right? (Is that called a gravity-feed waterer or something?) Anyways, it will be extremely cold here this winter and I am wondering if anyone has just made a waterer like this instead of buying the double-walled metal ones they sell.
Now if you think the stainless steel flat bowl will work out, is it important for the bottom of the bowl to be in complete contact with the heated tin top? Or doesn't it matter? Because it will have an air gap in between the tin and bowl unless I pound something out.

Thanks for any help.
Bridge - who asks questions that are clear as mud

 

[Bear Foot Farm]

Now if you think the stainless steel flat bowl will work out, is it important for the bottom of the bowl to be in complete contact with the heated tin top?

Youll get better heat transfer if there is full contact, but I would try it first without modifications.
You only need to keep it above 32 degrees. It doesnt have to be "warm"​

 

[BridgeTea]

Thank you, Bear. I agree, no need for warm water. I am just looking forward to NOT chipping the ice from a solid frozen bowl this year!