What I have done, used these in Powder coat ovens, heaters, rod ovens and now a keg cooker. Before a $7 oven element (4200 watts) is heated it is flexible, you can straighten it out, and reshape it. Keep it from touching itself thou or it will be a hot spot. I looked at the keg, it is made to completely "drain out one end" so I put the drain spickot on the bung hole end. Welded some legs onto it and called that part done. Later I welded some cut in half 1/2 npt couplings on the top for the sensors. Added a double boiler in top. (going to try to steam mash)
I created a outer housing from a old water tank from a well. Filled the area between the housing and the cut down keg with cerwool (mineral wool to some of you) like that comes in a old kitchen stove.
Controlling this? I have a industrial relay (old motor starter) tied in with a flip switch to "positively" kill both L1 and L2.. and then a SSR (cube relay) tied into a digital control with temp sensor. This breaks "one leg" turning the element on and off. I also have a local plug to disconnect it all.
So far it is all wonderful, keeps the heat up and steady 2 degrees (deadband setting in controller). I did a brew in a bag in the controller as a test and it worked out great. 5 gallons of water heats up with the 4200 watt element in about fifteen to twenty minutes. I have had 12 gallons to a hard boil in it, it took a bit longer.
My other option was a propane burner with a "gas heater" valve like they use in a furnace, this has built in "flame detection" with a thermopile, and a pilot light, you add a 24ac transformer and then you can switch it on and off with a temp control. My plan was to put this into my basement and I didn't want to vent it thou.
I knocked together that pvc box for the controller a year or two back, keep saying I am going to build a prettier one, I have been doing electrical work since I was young, fabricating machinery and equipment from scratch. It had cooked everything from jelly to tomato sauce, now on a beer cooker.
Tunnel Hill Ga. I'm a Old biker/construction worker, wore out, tired, relaxing with a homebrew and loving it. Ain't nothing like watching the sun come up over Fort Mountain.