Here is another stackable Raspberry Pi case for your DIY projects. The MaticBox4 Raspberry Pi 4 case can be mounted on flat surfaces, DIN rails, and any other object with zip ties. It supports 25x25mm fans and can be easily stacked for your cluster.
The case ships with two covers, so you are covered whether you are using one board or multiple ones in your project. MaticBox4 cases are available in multiple colors.