Thanks Wittie, some good tips on there that I, until now, was unaware of. I have just recently learned some tricks just by doing it to result in a nice frictionless spin for loose bb hubs. I guess my main concern on the tour is getting dirt and grime in the bearings and having it crap out on me in middle America. Am I being overly cautious to think this? Should I be prepared for something like this somewhere along the tour?
I wouldn't expect any problems for properly adjusted and greased bearings. They should last the distance of the TA without any attention, but if need be you could easily repack them along the way.
The mode of failure is most often pitted races because the bearings are allowed to run without grease. This will typically not stop you and leave you stranded. In most cases you could repack them possibly replacing the balls and continue to ride on them until you can conveniently replace them. If it came down to it you could ride the whole TA with pitted races.
Other more catastrophic failures are possibly, but not very common.
The bottom line is that even cheap hubs if properly maintained usually last a very long time and that maintenance does not need to be done very frequently. In all probability your rims will fail before your hubs, but that too is an infrequent occurrence unless you bend a rim in a collision..