For a heatstick, I installed a 20 Amp breaker and ran 12 gauge conduit to my outlet. Then I made a GFI extension cord (i.e. - a male plug -> conduit -> GFI outlet, all in a weather-proof box). Plugged in my heatstick (2000 watt 120 volt) to that and was good to go.
Heatsticks are also so versatile. Mine can heat up about 3 gallons to boiling in about 30 minutes (haven't timed it yet). They also come in handy if you don't hit your mash temp quite right. I use mine to break up grain, while heating if necessary. You can also just heat your strike water directly in your MLT (even if it's a cooler) if you put a bit of JB Weld on the end of the heatstick.
It would be only a couple extra steps to adapt these
heat stick directions (also linked in a previous post) to an electric keggle. As mentioned above, you'd absolutely need a GFI outlet, and to be sure that the elements are grounded to the keg. However, instead of going to all the trouble of installing the element(s) on the keg, why not just use a heatstick or two instead? Then you can also use the same one for the mash, sparge, ...
