Wow thats insulated better than most homes!
Theres enough water volume it looks like itll hold heat very well.
It would be cool to check it with an infared laser type thermometer if you have one. My buddy has one for working on hot rods we used to mess around with it. You can just point and shoot the thing all over and find your weak spots where the heat escapes. They are inexpensive iirc. Cheap at harbor freight if scientific accuracy isn't key.
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