Lots of people have made trash can smokers with, a trash can, cut either a hole in the bottom or made access door on side near bottom, used a hot plate or some form of electric heat element, and either a cast iron pan or some form of wood chip box.
The metallic coating will begin to melt around 427°C (800°F), and when heated to temperatures nearing boiling point, zinc oxide
fumes are produced. Boiling Point: 1663° F (907° C).
Most of your smoking is done with temps below 300º, and as long as your careful, there shouldn't be a problem.
Would I recommend making a trash can smoker, do you have $100? If you do then NO. If you make a trash can smoker and like the smoked product, it is just a matter of time before you buy a manufactured smoker. So instead of spending $35-40 for the stuff to put together a trash can, put that money toward a safe smoker.
You can buy this smoker for $70
This is a $170 smoker on sale, and it will smoke, grill, and not give you heavy metal poisoning.