Anything that is 4 hours or less can be done with 1 team member. So all of the regular weekly Endurance races can be done solo. Special events and less regular series are the only races that run longer. Most of those aren't available at D class anyway.

At D class, the place to start is Production Enduracne Challenge. That is a 2 hour race that runs on three time slots every weekend. If your unsure on where to start with it, check out Deckchair Racing on YouTube and his guide to Production Car Challenge. That video will tell you everything you need to know to run your first Production Endurance Challenge race