I'd crank it back to 5% a week, you have lots of time to ramp it up. A long ride now might be 16 to 20 miles. Do the specialized training rides like intervals and hill repeats during the week. Get the balance of miles on the weekend with back to back rides of roughly the same size. When they have worked up to 50-60 miles you are good to go. Drop back a bit the last week or two before the tour. The UMCA has a lot of info about training for long rides.