How do I Cost a Manual JE to a Project?

Summary: Interdepartmental JE to record Project-related Expenditures

Content (required): I need to post a journal entry to charge my PW department for parking passes on one of their projects. (DR: PW Exp, CR: Parking Rev). How can I also cost this against a project? In my test environment, I created a manual cost w spreadsheet and it seemed to work, but I don't know enough about projects to know if there is something else i would need to consider, or if it was really as easy and straight forward as it seemed.

If anyone could give me some guidance or point me toward some documentation to review. I've already looked at the "Using Project Costing" in the Help Center and got some good info, but I feel like I'm missing something.