I wouldn't.

1-2 week tour, not a big deal. 10 weeks, you need a bike that has low gearing, wide tires, fenders, heavy loads, rough pavement etc. (A typical TransAm is more like 3,000 - 4,000 miles btw)

You can get many brand-new touring bikes for $1000 or less; you can always sell it after the tour is over. Surly LHT, Jamis Aurora, Trek 520, REI Novara Randonee, etc are well-regarded and affordable bikes.

I'd go used if a) you're a decent mechanic and b) know what to look for in a touring frame.