The training challenge on a ride like this is both endurance and recovery. If you have ever rode an MS 150 you know that there are a lot fewer people riding day 2. A one day effort is far easier than having to recover and then do it again. On rides like the Bicycle Tour of Colorado (BTC) I see lots of riders making the mistake of not riding hard. You need to ride hard to finish sooner so that you avoid the heat, wind, and storms that come in the afternoon and to have longer to recover.
This ride is 113/day average with some pretty long 150 mile days. As a day ride, 113 miles isn't hard if you are conditioned. Twenty-six of them in a row is a different matter. The training plan has to build sustained endurance in order to cover the daily distance fast enough to allow time for recovery and has to stress the body so that it will recover.
I know this as block training.