My thought with the tires is that I'll sign up for Good Sam or AAA (I'll be browsing these forums for a comparison next...), so having a flat for the first ~2 months of the trip (while in the US, hopping from place to place, driving during the daytime through relatively good weather, etc) would be an inconvenience but not too bothersome. However, now that I'm thinking about the instance of a blowout and the damage it could do to my PW, new tires sound a lot more attractive. I'm glad I mentioned it, and thank you all for catching it!!
The Hercules looks like a fantastic tire and very reasonably priced, outstanding recommendation!
AGuyAndHisDog -- keep an eye on our blog, we'll be posting updates as we move across the country. If you save your Montana trip for August that's when we're expecting to be up there. Austin isn't exactly known for its camping, but you nailed it -- there are so many good spots just a few hours away from us! No name for our PW yet, but soon!