I asked something similar here. Like you, I wish there was a plan for ultra-endurance events but TR focuses a lot on shorter races.
I should definetely reply to my thread to show how it went tho. I’m back on SSB training for the same race this year (2600km in less than 10 days - aiming for 7 - in June) for the winter, and then I’ll probably keep 2 VO2max sessions per week with very long rides every week-ends.