I thought it was great and am hoping to do it again for 2020, and maybe Boulder as well.
I did exactly as @Bryce recommended, mid-volume:
SSB I and II
Sustained Power Build
I only did a few outside rides when I got to the century plan, none were more than 45 miles, and I didn’t do a single long climb. But thanks to TR I was plenty prepared to do the event. I’m planning to do the same training again this winter. I’m sure you’d be fine with Gen Build and/or Climbing Road Race Specialty too, but you only need sustained power as the climbs are long.
Note, it isn’t your typical fondo crowd that shows up at these events. 4 w/kg will put you mid-pack. @Jack_Russell_Racing had told me that before going, and i can confirm.
Super fun, highly recommended! Happy to answer any other questions.