I'm using my bluing tank right now - rain gutter. This is probably about the 12th barrel or so. Thats quite a few boil cycles for just a few dollars. You can see the end caps and how they are attached in the second photo. There is silicone in there too.
I use a 1 burner Coleman stove and a 2-burner stove as well. One day, I will cannibalize a propane grill for a burner. But for now, this works really really well with the things I already had on hand.
In the tank, I use a couple bent sections of 9 ga wire to hold the barrel off the bottom.
The barrel is polished to 600 grit or better and then washed with hot water and dish soap after being plugged with neoprene expandable plugs. Before it is treated the first time, it gets wiped down with alcohol or Acetone on paper towels.
The water is reverse-osmosis water, but that's not essential, I just happen to have it for other reasons. Tap water works too, but you will need to wipe down with EtOH quickly IMMEDIATELY after each boil to avoid water scale as the hot barrel dries. Scale will affect the evenness of the rusting and hence the finish of the blue. Holding the barrel vertical helps avoid drips that dry to cause scaling.
I use a wire carding wheel from Brownells in a hand held drill.
That's about it.
Brent
