Here's my latest installation, it uses Kal's o-ring inside washer method (blichmann) as he described in this thread. The element is 2000w 120v, and I've added a toggle switch. The box is an extension ring, not an actual box. This is thinner.
No silicone, nothing but the oring and metal-to-metal seating. I was able to tighten it down all the way, flattening the kettle wall.
The bolts run through the box extension holding the two covers and gaskets together on either side.