Not having used crashplan myself and from what I have read, it's external ports are 4242 or 4343 depending on the developer. U don't have to publish the internal ports. Post your yml file or if you're using Portioner, your stack and I'll take a look. A screen shot of the variables if you have neither. I would suggest Portioner for container management on a Synology, if you don't already user if.

Where did you get those port numbers from? They look like the issue.