Thanks so much for the great answers guys. After reading tons of stuff including your comments, I'm thinking I'll be fine with the 3-gallon case I bought for the trip. I haven't seen anything crazy in terms of consumption on my shorter trips, and my engine is in pretty good shape. I'll be on I-95 for a lot of the trip, so it'll probably be much easier to find straight 40-weight along the way than it was to get it here. I doubt I'll need it, but I'll probably pick some up because it's available. Before even reading about it here, I had noticed that my engine likes to run with the oil level slightly above the fill line on the dipstick. Anything above that disappears before too long, but it never gets any lower than that mark. That must be the "sweet spot" you guys are talking about. Scott - I've read about the oil reservoir in my parts book. Pretty cool. I kinda wish mine had that.
Thanks again for the great answers. After a few years on the board, I've found that the way to get people talking is to ask 'em about anything related to oil.