If you're heating directly then you probably won't be able to mount directly to the kettle, you'll likely melt the gasket you use to seal the element or even melt the insulation on the wires. I think a heatstick is your only option if you want to continue to direct fire.
After all this if you still want to mount an element in your kettle then bargainfittings has a locknut and gasket that you can use.
http://www.bargainfittings.com/index.php?route=product/product&path=36_38&product_id=95
You can also take a look at kal's Electric Brewery for some ideas
here.