There are three different approaches to improvising a sous-vide bath. These three methods are personified by three fictional characters.
Consider the simple act of fishing, using nothing more than parts scavenged from a junk yard (or from some backyards).
"The Martian" Mark Watney would "science the hell" of fishing, probably building a fish farm out of window screens and clock motors. Feeding the school with his own urine and feces.
McGyver would unwind copper wires from a car distributer, assemble a fishing rod from broomstick and a hook from a paper clip. Then go fishing
And a redneck? Throw in a stick of dynamite and scoop up dinner.
Now, each approach has its own merits, place and time. Not to mention legal implications. I tend towards the McGyver end of the scale, but let's give all three techniques a shot at improvised sous-vide.