I don't know a specific training plan perse but for a summer trip I did a few years ago I followed a conditioning regime that started in the spring. Much of it to get used to spending long hours in the saddle
- Because I work Mon-Fri I rode to work each day just to get saddle time (15km)
- One or two times a week I would take the long way home and stretch it to an hour or so of riding.
- On the weekends I would select a day route that gradually increased the distance starting from say 30 - 100km's. That became my relaxing day of bike touring. Fortunately I live in a great place with a lot of variety.
- Then I began increasing the difficulty of those day rides by adding hills. 1 hour away I have access to 3 mountain passes and a coastal hwy. I tried to make it fun by inviting friends along for some of them.
First:
Then:
Working up to this: