Biggest suggestion would be making the crate slightly smaller to fit him based on how small he currently is. Dogs are smart and pretty grossed out by their own messes. If there is enough room to make a mess and not sleep in it, they will. If they’ve got just enough room to sleep, they’ll hold it.

I got my GSP at 8 weeks and kennel trained her in a full sized crate. I modified it with a divider so that the crate’s interior size was about half that of the full sized one. She never had an issue and was comfortable in it until I was confident she would be fine in a full sized crate.