Recently my interest was piqued with a very long tour: http://tourdivide.org/
Being time constrained by an 8 hour job, how does one train for a ride that will require 160 kilometers (100 miles) per day for 30 days?
I confess, I have not done this kind of ride. But I know a few folks who have done some long ones: Vancouver, BC to San Diego; San Francisco to the Mexican Border; the 999 Ride, and so forth.
I will tell you a few things they passed along to me.
You do not mention any particular experience with this kind of riding, so you may want to do some shorter rides-- 500 miles or whatever-- before attempting such a long, hard ride.
If you are doing loaded touring on windy and/or hilly roads you may only average 8 mph, so you might be in the saddle a lot longer.
To be comfortable on a bike for that long you need only a few things: good shorts, a good saddle, good chamois cream and reasonably strong legs.
Padding in normally bad for both the saddle and the chamois in your shorts as it allows pressure to be placed on more of your skin. You really want most of the pressure to be on your Sitz bones (ischial tuberosity). You need a good cream to keep you from chafing or getting saddle sores (boils). The stronger your legs are the more weight you can keep on them and off your saddle.
As for training, if you can ride for 2 hour with out ANY discomfort you should not have trouble riding 100 with a higher level of discomfort.
The problem I see you having is that you are going to be on the edge of your distance everyday and won't really be able to enjoy the trip. I would cut the distance in half and enjoy myself along the way.