These are popular in the UK, but I have not seen them much elsewhere, and are in fact on my list of "to get next" brew gear.
If I could easily get an element fitted I wouldn't hesitate.
It is basically a double skinned 80L stainless steel pot (though lots of smaller sized ones are available), that is fully insulated.
This thread
here shows how one was cut up to suit.
Very similar to your idea cooldood, but with stainless.