Here are a couple of pics of one I made, using a 20MM ammo box, with charcoal as the heat source. It works extremely well. I have used it on pipe up to 1" Sched 80. I expect it will also work on larger sizes. There has not been a need to rotate the pipe (though rotating never hurts!)
It is important that you raise the box off the ground, or there will be heat damage. In the first pic, you can see that I've used short pieces of strut for this purpose.
I have also had to replace the rubber gasket with one made of stove gasket material. When I am finished, I simply close it up to extinguish the coals; they can be used again. The only drawback is that it takes a fair amount of time for this thing to cool down enough for safe transport.
[This message has been edited by renosteinke (edited 12-25-2006).]