The drum heater at the above link has an interesting thing in their ad. It says that it works on plastic, metal or fiber drums.
Umm, two different products advertised on that page.
The "induction drum heater" is for steel drums, you know, the 55-gallon kind. Induction, of course, will work fine on a steel drum.
The product that works on plastic and fiber is the "LMK Flexible Heating Jacket", which is an entirely different animal that does not work by induction.