A fellow rider and I are training also - we have 6 weeks to go and are up to 60 miles. I ride three times a week - Wednesday, Friday and Sunday. 60 still feels a little rough, so I'm a little concerned because I am certain there is a huge difference between 60 and 80, and again between 80 and 100!
I was going to try adding 5-7 miles per week, depending on the amount of incline the route offers. Food/fuel might be an obstacle for me to sort out now - what do you usually carry? Right now I have one water bottle with Nunn in it, the other is plain water, when we refill I do the same, first bottle is Nunn the other plain. I carry peanuts and home-made fruit roll ups. I usually also have a peanut butter granola bar along.