Preparing for a 400km randonnée

I’m looking to participate in a mountainous 400km randonnée next year involving 9000m of climbing. The time limit is 24 hours. Does anyone have any experience of using TR to prepare for such an event?

Also doing my first 400km in May. I just use TR as a general fitness and weight management tool rather than a specific tool. I am doing ‘climbing road race’ at the mo. I got bored doing the ‘century’ plan.

Tell us about your event. Mine is roughly Bristol to London and back via some lumps. Flat in comparison to yours with only about 3000m elevation. Part of the ‘Billiard Table’ series of rides a local rider puts on. 27 hour limit.