I'm just reporting back, for anyone who wants to bring wine on board in the future and sees this thread. It was perfectly simple.   I didn't have to walk my three cases through security, or anything at all, really. The porters took them from me when I arrived, and that was that.   In the Seattle terminal there was no desk for paying corkage, so I just went to the front desk and told them that I had brought three cases on board. I kept one case with me, and the dining room has the other two.