I have ready this directions for break in that comes with the unit but also seem to recall people wiping cooking oil all over the inside. Any thoughts are recommendations?
Lots of people spray with cooking spray which is fine. I just did a pork butt. It will get seasoned all on its own as you use it. So spray or not. Good luck.
The burn in pretty much gets rid of all contaminates. I used peanut oil for the outside (Kinda gives an even newer look...if that's possible), Many think oiling the inside or cooking bacon will help cure but in the end, the eventual cooks will do the curing for you. Doesn't hurt to pre-oil but either way in a month or so you will never tell the difference.
I sprayed the inside of mine with cooking spray, but agree with others it wasn't really necessary unless you plan to let your 640 sit for a long, long time without use. Mine was more than seasoned within a couple of days of its arrival.