I remember I've had this topic some time ago.
I could imagine nothing has changed about it if the rclone-docker docu doesn't ship with an example and mentioning of multiple mounts in a single docker.
Specifically that means it is designed to have one mount per container and the linked docker-compose could help you having work minimized still tho.
I do need to admit that I actually never transfered over to rclone in docker. So I have no practical experience.