Need help making a forced air heater
You should buy a cheap heater instead of doing this possibly very dangerous machine, but:

You could probably use a UL94 V0 plastic of some sorts for the enclosure. But I would place the metal wire construction on a separate metal frame inside the plastic housing, with some distance between them. Of course with a metal frame for the wires, you need to think of a way of routing them so they don't short circuit. 

And also make totally sure that no metal parts can be touched from the outside. You should also add overheating and short circuit protection of some sorts. A PTC fuse for the overheating and a "normal" ceramic/glass fuse for the short circuit. All cables inside the housing that leads to the Kanthal wires must have insulation that can withstand high temperature.

UL 94 classification:


  V-0: burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.