with an immersion chiller, you really only need to worry about the outside. Vinegar will do the job as well a few other cleaner/sanitzers. I use PBW and Starsan. I sanitive before I put it into my boil. It is overkill, but it puts my mind at ease.
Keg 1: American Wheat
Keg2: German Ale
Next up: Christmas Old Ale, American Wheat AG, need suggestions