Karsten was logged in the last time three years ago, possibly he moved on.
I’ll try to reply for him, most likely he used that bag:
https://www.amazon.de/Aosbos-Isolierte-Lunchbox-Kühltasche-wiederverwendbare/dp/B07VWQF9K8/
I can confirm that the given bag dimensions will match to the Strida rack.