I mash in a 15 gallon stainless steel kettle with a bazooka tube and ball valve. I wrap the kettle in Reflectix, which I bought at Lowe's (maybe it was HD but I think they both sell it). It maintains temp very well even when it's really cold outside. If I miss mash temp after doughing in, I can just turn the flame back on and bump the temp back up to where I need it before closing it up and wrapping it. I like that better than having to add hot or cold water to my mash tun to adjust my mash temp.