Eating and drinking enough is almost as much of a challenge as the riding will be. Scratch that - it's more of a challenge. If you're tough and persistent, and prepared to change lots of flat tires, the riding part is probably do-able. But keeping your body fueled and hydrated is not a matter of toughness, it's a matter of knowing how much and how often. You'll have to learn real quick how many hundred calories per hour you need and what kind of food your stomach can process while riding, and how much and what kind of fluid to drink. This is true for a single century, and magnified for back to backs.

Figure out the eating and hydration part, ride from dawn to dusk, and you'll get it done. Bonk or get dehydrated and you'll be done.