I decided to order a cap for my velomobile at a webshop ; velomobielonderdelen (“velomobile-parts” in English). The famous Wim Schermer is starting the production of these caps soon. He thinks the production will be about three per week. It’s not cheap, but I’m not able to make them better and cheaper myself. Wim (and his friends) have optimised the model after a lot of experimenting kilometers.