I would highly recommend recumbent trikes for long touring such as this. While recumbents can be a bit more pricey (anywhere from $800 - $3000 for a decent touring model, depending on brand), your butt, arms, shoulders, neck, and back will thank you for it. Not to mention you'll see more of the countryside instead of staring at the road ahead. And be able to travel farther on a daily basis due to the comfort. And not worry about falling over with a heavy touring load.
Dealers around the US:
http://www.catrike.com/dealers.php - $2000-$3000
http://www.terratrike.com/ (dealer page is under 'Products') - $1000-$1600 for base tour models
http://www.icetrikes.co/home - $2800 for their folding touring trike
http://www.kmxus.com/models/ - for young tour cyclists or off-road.
http://www.getitbent.com/arrow.html
http://www.t-ryx.com/trikes.htm
You may also want to check out the website of the recent "Roll Over America" tour (
http://web.mac.com/josef.janning/Roll_over_America/Home.html). West-coast to east-coast in 4 weeks by a large group of velomobile riders. The site has a route map, blogs, and experiences of the tour that are worth reading about, at least for an insight as to the experiences of many riders.