I cyclecamped for 2-3 weeks a year for about 10 or 12 years - IMHO you would have the least pain such as those mentioned in the training shedule if you just take maybe 3 or 4 months, and every week do two rides, starting with the longest mileage you are currently comfortable, and increase that distance 5 miles or so every other week. When you get to being able to do 50 miles over mixed terrain with no pain, your body is probably ready. Learn how to load the bike for touring so that the weight is evenly distributed.
My recollection is that when I didn't do this preparation before my tours, I'd have a pain in the sitzplatz that took a week to get over. Remember, you're likely to average 10mph... so it's your seat and your arms that will protest the most if you haven't prepared.