As others have mentioned, there are many kinds of stainless steel, some being more rust resistant than others. I hate to call anything rust proof, because there are things that will rust that stainless steel in no time. But living in Austin which I assume is a drier air, you should be fine. Seasoning is also done just to burn out any impurities in the drum. For all you know that drum held pickles, who wants a pickle flavor in their food? Burn it out at a higher temperature than you normally cook, to get any nasty flavor out of it. You don't necessarily have to start a huge bonfire in it, load it with charcoal and open all the intakes, let it cruise up to its high temperature and sit there.
I wouldn't worry about where you cut into the drum either.
XL Big Green Egg, Weber Performer Platinum, WSM 22.5"