You may consider a recumbent bicycle. They are realy comfortable for those long rides.
More and more people are chosing bents nowadays. At least test ride a few. Don't just limit yourself to uprights. I'm NOT going to say you'll like them better, but if you're looking for a bike I think the comfort that a bents offer makes them major contenders as touring bikes.
Also, their is more variety in terms of frame design. Uprights all have that double diamond design. Bent's have short wheel based machines, long wheel base, tadpole trikes, delta trikes, above seat steering, below seat steering
My favorite companies are:
Rans,
Tour Easy, and
Cycle Genius