Just picked up a 10.5 gallon Bayou pot for my foray into all-grain BIAB.
I decided to kill two birds with one stone and leak test the weldless kettle valve I installed and see how much heat loss I'd see with it at mashing temps.
First: No leaks from the kettle valve!
Second: Heat loss wasn't bad at all. Filled the kettle with ~10 gallons of hot water right from the tap (Which was 153.6 degrees! Have since turned my water heater thermostat down). Started at 153.6 degrees. Put the cover on, and wrapped it in a beach towel. This is all in my kitchen, at 70 degrees ambient. 30 minutes later, unwrapped, uncovered, and stirred it up to make sure there wasn't any stratification. 150.1 degrees, a 3.5 degree loss. With a better wrap I don't see heat loss being an issue at all.
Third: An unexpected benefit. The inside of the pot and basket developed a tan oxidation layer from the soak in hot water. I re-wrapped it and let it sit for another hour, looks like it's all set to BIAB now.
Now if mother nature would co-operate and warm up a bit outside...