The APU? The manufacturer also sells cheap metal cases that double as heatsinks, check out the webshop. The black one has the best heat-dissipation. If you want to fit 2.5" disks you'll have to DIY a bit.

E.g. here: https://www.pcengines.ch/newshop.php?c=2 - the type of the case is listed under "use with" on the product page.