Custom Keg Work for HERMS, need advice

I posted this in DIY, but thought I might have more luck getting info here.

I'd like to have a keg converted to a HLT for use on my HERMS system. I have a question regarding what size hole and what type of fitting I should have installed for the heating element.
I use a 5500watt heating element currently and would like to stick to the same thing. What size hole will they need to place for this? Also, whats the best way to attach the heating element to the keg? Should I have them put a threaded port of some sort?
My main goal is to have a nice clean installation with an easily removable heating element for any sort of servicing or replacement and for cleaning purposes. I just don't know the best way to have this done. I'm having it welded professionally for a nice clean weld on the inside.
Any ideas? If you have any pics to help me see what you're talking about that would be very helpful. Thanks!

I have my nut welded directly onto the Keg so I just thread the element in and out when I need to. I probably have a picture somewhere if not I'll attach what mine looks like