Congratulations on being selected to participate in this challenging series of rides!
The only piece of advice I can give you is consider buying a trainer. Yes, I've seen your earlier posts in which you state that riding on a trainer is too boring. All I can say is, I bought my trainer at Christmas last year, and since then, my cycling fitness has experienced a quantum leap. During the harsh winter months or during other periods of foul weather, having the trainer enabled me to ride hard nearly every day of the week.
Good luck on your training program and we look forward to hearing about your participation in this epic ride.