Stretching and increasing your fitness level can help, but nutrition is the key. I had cramping issues until I became aware of the need for potassium and sodium as distance increases. Gatorade will not give you enough. You can get supplements at most bike shops, like Endurolyte, Elete, Saltstick, etc. You should also choose helpful foods before/during rides, like almonds, potato chips, etc.

I was able to pedal for 23 hours straight without cramps. With proper nutrition/hydration, you will fall asleep on the bike before cramping up. Try searching or asking the long distance forum for more info.

Commuting is a great way to get in miles if it can work for you. An hour on the bike vs. 30 minutes in the car makes for a "free" half hour of training every day.

The Centurion is more than enough bike to get you there, if it is in good condition. Equipment choices are not that critical to getting the distance, as long as the bike is road-worthy. Good luck, and enjoy the training and the ride.