Help me build a plan to build power/endurance for long solo rides

I would like to be able to sustain high power for 5 hour rides. Minimal climbing and little to no stops on country roads.

I was thinking of modifying the existing plans but which workouts should I swap from base and build? I can do one long ride and 4 45-60 min workouts a week.

Why would you swap any workouts?

Could you tell us more about yourself and your training history and why the current plans or Plan Builder aren’t suitable?

Do I really need to do over/under and vo2max workouts?

How are these helping me if I plan to never go above threshold? I used to do these last season and I’m not sure they helped me. Maybe I’m missing something?

Over-under and V02 max workouts will increase your threshold.

So even if you never ride over threshold, 90% of a 250w threshold is still higher than 90% of a 200w threshold.

You can train to maintain higher percentages of FTP for longer durations, but I suspect that FTP gains will come easier and with more variety/fun.

Look at the plans for long distance steady state athletes like “sustained power build” or any of the “full distance triathlon” plans and you will find plenty of V02 max work. Yet these are aimed at athletes who, when racing, won’t be going over threshold if they can help it